Add simple MediaSourceAttachment class (#3232)

Registers `MediaSource` objects to the `MediaSourceRegistry` through a
`MediaSourceAttachment` proxy. The new `MediaSourceAttachment` class is
cross-thread reference counting safe, unlike `MediaSource`, which will
allow for utilizing `MediaSource` objects created on Dedicated Workers.

This change does not add any additional functionality, and is intended
as an incremental update towards enabling the creation of `MediaSource`
objects on Dedicated Worker threads.

See [Chromium's `MediaSourceAttachment` interface][1], and the commit
that [initially introduced it][2].

[1]:
https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/html/media/media_source_attachment.h
[2]: https://chromium-review.googlesource.com/c/chromium/src/+/2300804

b/338425449

Change-Id: I016c010c9ef4a0e576bd67ce584d75dbe75986ec
(cherry picked from commit 29e0d65)

cobalt/browser/web_module.cc

@@ -52,6 +52,7 @@
 #include "cobalt/dom/keyboard_event.h"
 #include "cobalt/dom/keyboard_event_init.h"
 #include "cobalt/dom/local_storage_database.h"
+#include "cobalt/dom/media_source_attachment.h"
 #include "cobalt/dom/mutation_observer_task_manager.h"
 #include "cobalt/dom/navigation_type.h"
 #include "cobalt/dom/navigator.h"
@@ -417,7 +418,7 @@ class WebModule::Impl {
   dom::MutationObserverTaskManager mutation_observer_task_manager_;
 
   // Object to register and retrieve MediaSource object with a string key.
-  std::unique_ptr<dom::MediaSource::Registry> media_source_registry_;
+  std::unique_ptr<dom::MediaSourceAttachment::Registry> media_source_registry_;
 
   // The Window object wraps all DOM-related components.
   scoped_refptr<dom::Window> window_;
@@ -584,7 +585,7 @@ WebModule::Impl::Impl(web::Context* web_context, const ConstructionData& data)
       web_context_->name(), data.options.track_event_stats));
   DCHECK(web_module_stat_tracker_);
 
-  media_source_registry_.reset(new dom::MediaSource::Registry);
+  media_source_registry_.reset(new dom::MediaSourceAttachment::Registry);
 
   const media::DecoderBufferMemoryInfo* memory_info = nullptr;
 

cobalt/dom/BUILD.gn

@@ -194,6 +194,7 @@ static_library("dom") {
     "media_settings.cc",
     "media_source.cc",
     "media_source.h",
+    "media_source_attachment.h",
     "memory_info.cc",
     "memory_info.h",
     "mime_type_array.cc",

cobalt/dom/dom_settings.h

@@ -39,14 +39,14 @@ class GlobalEnvironment;
 class JavaScriptEngine;
 }  // namespace script
 namespace dom {
-class MediaSource;
+class MediaSourceAttachment;
 class Window;
 
 // A package of global state to be passed around to script objects
 // that ask for it in their IDL custom attributes.
 class DOMSettings : public web::EnvironmentSettings {
  public:
-  typedef web::UrlRegistry<MediaSource> MediaSourceRegistry;
+  typedef web::UrlRegistry<MediaSourceAttachment> MediaSourceRegistry;
   // Hold optional settings for DOMSettings.
   struct Options {
     // Microphone options.

cobalt/dom/html_element_context.h

@@ -42,14 +42,14 @@ namespace cobalt {
 namespace dom {
 
 class HTMLElementFactory;
-class MediaSource;
+class MediaSourceAttachment;
 
 // This class contains references to several objects that are required by HTML
 // elements, including HTML element factory, which is used to create new
 // HTML elements.
 class HTMLElementContext {
  public:
-  typedef web::UrlRegistry<MediaSource> MediaSourceRegistry;
+  typedef web::UrlRegistry<MediaSourceAttachment> MediaSourceRegistry;
 
 #if !defined(COBALT_BUILD_TYPE_GOLD)
   // No-args constructor for tests.

cobalt/dom/html_media_element.cc

@@ -40,6 +40,7 @@
 #include "cobalt/dom/html_video_element.h"
 #include "cobalt/dom/media_settings.h"
 #include "cobalt/dom/media_source.h"
+#include "cobalt/dom/media_source_attachment.h"
 #include "cobalt/dom/media_source_ready_state.h"
 #include "cobalt/loader/fetcher_factory.h"
 #include "cobalt/media/url_fetcher_data_source.h"
@@ -892,8 +893,16 @@ void HTMLMediaElement::LoadResource(const GURL& initial_url,
       return;
     }
 
-    media_source_ =
+    scoped_refptr<MediaSourceAttachment> attachment =
         html_element_context()->media_source_registry()->Retrieve(url.spec());
+
+    if (!attachment) {
+      NoneSupported("Media source is NULL.");
+      return;
+    }
+
+    media_source_ = attachment->media_source();
+
     if (!media_source_) {
       NoneSupported("Media source is NULL.");
       return;

cobalt/dom/media_source.h

@@ -67,7 +67,6 @@
 #include "cobalt/script/environment_settings.h"
 #include "cobalt/script/exception_state.h"
 #include "cobalt/web/event_target.h"
-#include "cobalt/web/url_registry.h"
 #include "media/filters/chunk_demuxer.h"
 
 namespace cobalt {
@@ -79,7 +78,6 @@ namespace dom {
 class MediaSource : public web::EventTarget {
  public:
   typedef ::media::ChunkDemuxer ChunkDemuxer;
-  typedef web::UrlRegistry<MediaSource> Registry;
 
   // Custom, not in any spec.
   //

cobalt/dom/media_source_attachment.h

@@ -0,0 +1,56 @@
+// Copyright 2024 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef COBALT_DOM_MEDIA_SOURCE_ATTACHMENT_H_
+#define COBALT_DOM_MEDIA_SOURCE_ATTACHMENT_H_
+
+#include "base/memory/ref_counted.h"
+#include "cobalt/dom/media_source.h"
+#include "cobalt/script/tracer.h"
+#include "cobalt/web/url_registry.h"
+
+namespace cobalt {
+namespace dom {
+
+// Interface for potential cross-context management of MediaSource objects.
+// Used with the MediaSourceRegistry for attaching MediaSources to media
+// elements.
+class MediaSourceAttachment
+    : public base::RefCountedThreadSafe<MediaSourceAttachment>,
+      public script::Traceable {
+ public:
+  typedef web::UrlRegistry<MediaSourceAttachment> Registry;
+
+  explicit MediaSourceAttachment(scoped_refptr<MediaSource> media_source)
+      : media_source_(media_source) {}
+
+  scoped_refptr<MediaSource> media_source() const { return media_source_; }
+
+  void TraceMembers(script::Tracer* tracer) override {
+    tracer->Trace(media_source_);
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<MediaSourceAttachment>;
+  ~MediaSourceAttachment() = default;
+
+  scoped_refptr<MediaSource> media_source_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSourceAttachment);
+};
+
+}  // namespace dom
+}  // namespace cobalt
+
+#endif  // COBALT_DOM_MEDIA_SOURCE_ATTACHMENT_H_

cobalt/dom/url_media_source.cc

@@ -17,6 +17,7 @@
 #include "cobalt/base/polymorphic_downcast.h"
 #include "cobalt/dom/dom_settings.h"
 #include "cobalt/dom/media_source.h"
+#include "cobalt/dom/media_source_attachment.h"
 #include "cobalt/web/context.h"
 #include "cobalt/web/environment_settings.h"
 #include "cobalt/web/url.h"
@@ -34,7 +35,11 @@ void RegisterMediaSourceObjectURL(
       base::polymorphic_downcast<dom::DOMSettings*>(environment_settings);
   DCHECK(dom_settings);
   DCHECK(dom_settings->media_source_registry());
-  dom_settings->media_source_registry()->Register(blob_url, media_source);
+
+  scoped_refptr<MediaSourceAttachment> attachment =
+      base::MakeRefCounted<MediaSourceAttachment>(media_source);
+
+  dom_settings->media_source_registry()->Register(blob_url, attachment);
 }
 
 // extern

cobalt/dom/window.cc

@@ -37,7 +37,7 @@
 #include "cobalt/dom/input_event.h"
 #include "cobalt/dom/keyboard_event.h"
 #include "cobalt/dom/location.h"
-#include "cobalt/dom/media_source.h"
+#include "cobalt/dom/media_source_attachment.h"
 #include "cobalt/dom/mouse_event.h"
 #include "cobalt/dom/mutation_observer_task_manager.h"
 #include "cobalt/dom/navigator.h"
@@ -102,7 +102,7 @@ Window::Window(
     script::ExecutionState* execution_state,
     script::ScriptRunner* script_runner,
     script::ScriptValueFactory* script_value_factory,
-    MediaSource::Registry* media_source_registry,
+    MediaSourceAttachment::Registry* media_source_registry,
     DomStatTracker* dom_stat_tracker, const std::string& font_language_script,
     const base::Callback<void(const GURL&)> navigation_callback,
     const loader::Decoder::OnCompleteFunction& load_complete_callback,

cobalt/dom/window.h

@@ -93,7 +93,7 @@ class Element;
 class History;
 class LocalStorageDatabase;
 class Location;
-class MediaSource;
+class MediaSourceAttachment;
 class Navigator;
 class OnScreenKeyboard;
 class Performance;
@@ -119,7 +119,7 @@ class Window : public web::WindowOrWorkerGlobalScope,
   // base::TimeDelta parameter will contain the document's timeline time when
   // close() was called.
   typedef base::Callback<void(base::TimeDelta)> CloseCallback;
-  typedef web::UrlRegistry<MediaSource> MediaSourceRegistry;
+  typedef web::UrlRegistry<MediaSourceAttachment> MediaSourceRegistry;
   typedef base::Callback<void(const std::string&,
                               const base::Optional<std::string>&)>
       CacheCallback;