[BreakoutBox] Add MediaStreamTrackProcessor

This CL introduces MediaStreamTrackProcessor, an object that allows
exposing a MediaStreamTrack's media frames as a readable stream,
enabling applications to perform custom processing.
This basically allows the creation of a custom sink, in terms of the
model proposed by the Media Capture and Streams spec [1].
A MediaStreamTrackProcessor can be combined with a TransformStream and a
MediaStreamTrackGenerator to effectively insert a processing step inside
an existing track.

[1] https://w3c.github.io/mediacapture-main/#the-model-sources-sinks-constraints-and-settings

Bug: 1142955
Change-Id: I2a119f0c2ea9ce50432509286bd0f43758d8a272
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2524322
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826153}

third_party/blink/public/mojom/web_feature/web_feature.mojom

@@ -3055,6 +3055,7 @@ enum WebFeature {
   kV8HTMLDialogElement_ShowModal_Method = 3726,
   kAdFrameDetected = 3727,
   kMediaStreamTrackGenerator = 3728,
+  kMediaStreamTrackProcessor = 3729,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/bindings/generated_in_modules.gni

@@ -1679,6 +1679,8 @@ generated_interface_sources_in_modules = [
   "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_media_stream_track_event.h",
   "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_media_stream_track_generator.cc",
   "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_media_stream_track_generator.h",
+  "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_media_stream_track_processor.cc",
+  "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_media_stream_track_processor.h",
   "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_merchant_validation_event.cc",
   "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_merchant_validation_event.h",
   "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_metadata.cc",

third_party/blink/renderer/bindings/idl_in_modules.gni

@@ -384,6 +384,7 @@ static_idl_files_in_modules = get_path_info(
           "//third_party/blink/renderer/modules/mediastream/media_stream_track_event.idl",
           "//third_party/blink/renderer/modules/mediastream/media_stream_track_event_init.idl",
           "//third_party/blink/renderer/modules/mediastream/media_stream_track_generator.idl",
+          "//third_party/blink/renderer/modules/mediastream/media_stream_track_processor.idl",
           "//third_party/blink/renderer/modules/mediastream/media_track_capabilities.idl",
           "//third_party/blink/renderer/modules/mediastream/media_track_constraint_set.idl",
           "//third_party/blink/renderer/modules/mediastream/media_track_constraints.idl",

third_party/blink/renderer/modules/BUILD.gn

@@ -349,6 +349,7 @@ source_set("unit_tests") {
     "mediastream/media_stream_constraints_util_video_device_test.cc",
     "mediastream/media_stream_device_observer_test.cc",
     "mediastream/media_stream_track_generator_test.cc",
+    "mediastream/media_stream_track_processor_test.cc",
     "mediastream/media_stream_video_capturer_source_test.cc",
     "mediastream/media_stream_video_renderer_sink_test.cc",
     "mediastream/media_stream_video_source_test.cc",

third_party/blink/renderer/modules/mediastream/BUILD.gn

@@ -56,6 +56,8 @@ blink_modules_sources("mediastream") {
     "media_stream_track_event.h",
     "media_stream_track_generator.cc",
     "media_stream_track_generator.h",
+    "media_stream_track_processor.cc",
+    "media_stream_track_processor.h",
     "media_stream_utils.cc",
     "media_stream_utils.h",
     "media_stream_video_capturer_source.cc",

third_party/blink/renderer/modules/mediastream/idls.gni

@@ -11,6 +11,7 @@ modules_idl_files = [
   "media_stream_track.idl",
   "media_stream_track_event.idl",
   "media_stream_track_generator.idl",
+  "media_stream_track_processor.idl",
   "overconstrained_error.idl",
 ]
 

third_party/blink/renderer/modules/mediastream/media_stream_track_processor.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "third_party/blink/renderer/modules/mediastream/media_stream_track_processor.h"
+
+#include "third_party/blink/public/mojom/web_feature/web_feature.mojom-blink.h"
+#include "third_party/blink/renderer/core/execution_context/execution_context.h"
+#include "third_party/blink/renderer/core/streams/readable_stream.h"
+#include "third_party/blink/renderer/modules/mediastream/media_stream_utils.h"
+#include "third_party/blink/renderer/modules/mediastream/media_stream_video_track.h"
+#include "third_party/blink/renderer/modules/mediastream/media_stream_video_track_underlying_source.h"
+#include "third_party/blink/renderer/platform/bindings/exception_state.h"
+#include "third_party/blink/renderer/platform/bindings/script_state.h"
+#include "third_party/blink/renderer/platform/instrumentation/use_counter.h"
+#include "third_party/blink/renderer/platform/wtf/uuid.h"
+
+namespace blink {
+
+MediaStreamTrackProcessor::MediaStreamTrackProcessor(
+    ScriptState* script_state,
+    MediaStreamComponent* input_track)
+    : input_track_(input_track) {
+  DCHECK(input_track_);
+  UseCounter::Count(ExecutionContext::From(script_state),
+                    WebFeature::kMediaStreamTrackProcessor);
+}
+
+ReadableStream* MediaStreamTrackProcessor::readable(ScriptState* script_state) {
+  DCHECK_EQ(input_track_->Source()->GetType(), MediaStreamSource::kTypeVideo);
+  if (!source_stream_)
+    CreateVideoSourceStream(script_state);
+  return source_stream_;
+}
+
+void MediaStreamTrackProcessor::CreateVideoSourceStream(
+    ScriptState* script_state) {
+  DCHECK(!source_stream_);
+  video_underlying_source_ =
+      MakeGarbageCollected<MediaStreamVideoTrackUnderlyingSource>(script_state,
+                                                                  input_track_);
+  source_stream_ = ReadableStream::CreateWithCountQueueingStrategy(
+      script_state, video_underlying_source_, /*high_water_mark=*/0);
+}
+
+MediaStreamTrackProcessor* MediaStreamTrackProcessor::Create(
+    ScriptState* script_state,
+    MediaStreamTrack* track,
+    ExceptionState& exception_state) {
+  if (!track) {
+    exception_state.ThrowDOMException(DOMExceptionCode::kOperationError,
+                                      "Input track cannot be null");
+    return nullptr;
+  }
+
+  if (track->kind() != "video") {
+    exception_state.ThrowDOMException(DOMExceptionCode::kNotSupportedError,
+                                      "Only video tracks are supported");
+    return nullptr;
+  }
+
+  if (!script_state->ContextIsValid()) {
+    exception_state.ThrowDOMException(DOMExceptionCode::kNotSupportedError,
+                                      "The context has been destroyed");
+
+    return nullptr;
+  }
+
+  return MakeGarbageCollected<MediaStreamTrackProcessor>(script_state,
+                                                         track->Component());
+}
+
+void MediaStreamTrackProcessor::Trace(Visitor* visitor) const {
+  visitor->Trace(input_track_);
+  visitor->Trace(video_underlying_source_);
+  visitor->Trace(source_stream_);
+  ScriptWrappable::Trace(visitor);
+}
+
+}  // namespace blink

third_party/blink/renderer/modules/mediastream/media_stream_track_processor.h

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef THIRD_PARTY_BLINK_RENDERER_MODULES_MEDIASTREAM_MEDIA_STREAM_TRACK_PROCESSOR_H_
+#define THIRD_PARTY_BLINK_RENDERER_MODULES_MEDIASTREAM_MEDIA_STREAM_TRACK_PROCESSOR_H_
+
+#include "third_party/blink/renderer/modules/mediastream/media_stream_track.h"
+#include "third_party/blink/renderer/modules/modules_export.h"
+#include "third_party/blink/renderer/platform/bindings/script_wrappable.h"
+#include "third_party/blink/renderer/platform/heap/impl/heap.h"
+
+namespace blink {
+
+class MediaStreamComponent;
+class MediaStreamVideoTrackUnderlyingSource;
+class ScriptState;
+class ReadableStream;
+
+class MODULES_EXPORT MediaStreamTrackProcessor : public ScriptWrappable {
+  DEFINE_WRAPPERTYPEINFO();
+
+ public:
+  static MediaStreamTrackProcessor* Create(ScriptState*,
+                                           MediaStreamTrack*,
+                                           ExceptionState&);
+  MediaStreamTrackProcessor(ScriptState*, MediaStreamComponent*);
+  MediaStreamTrackProcessor(const MediaStreamTrackProcessor&) = delete;
+  MediaStreamTrackProcessor& operator=(const MediaStreamTrackProcessor&) =
+      delete;
+
+  // MediaStreamTrackProcessor interface
+  ReadableStream* readable(ScriptState* script_state);
+
+  MediaStreamComponent* input_track() { return input_track_; }
+
+  void Trace(Visitor* visitor) const override;
+
+ private:
+  void CreateVideoSourceStream(ScriptState* script_state);
+
+  Member<MediaStreamComponent> input_track_;
+  Member<MediaStreamVideoTrackUnderlyingSource> video_underlying_source_;
+  Member<ReadableStream> source_stream_;
+};
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_RENDERER_MODULES_MEDIASTREAM_MEDIA_STREAM_TRACK_PROCESSOR_H_

third_party/blink/renderer/modules/mediastream/media_stream_track_processor.idl

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// See spec in developement at
+// https://w3c.github.io/mediacapture-insertable-streams/
+[
+    Exposed=Window,
+    RuntimeEnabled=MediaStreamInsertableStreams
+]
+interface MediaStreamTrackProcessor {
+  [CallWith=ScriptState, RaisesException, MeasureAs=MediaStreamTrackProcessor]
+  constructor(MediaStreamTrack track);
+
+  // This stream returns VideoFrame objects.
+  // TODO(crbug.com/1142955): Add support for audio.
+  [CallWith=ScriptState] readonly attribute ReadableStream readable;
+
+  // TODO(crbug.com/1142955): Add |writable| attribute that takes control signals.
+};

third_party/blink/web_tests/webexposed/global-interface-listing-expected.txt

@@ -5182,6 +5182,10 @@ interface MediaStreamTrackGenerator : MediaStreamTrack
     attribute @@toStringTag
     getter writable
     method constructor
+interface MediaStreamTrackProcessor
+    attribute @@toStringTag
+    getter readable
+    method constructor
 interface MerchantValidationEvent : Event
     attribute @@toStringTag
     getter methodName

tools/metrics/histograms/enums.xml

@@ -30231,6 +30231,7 @@ Called by update_use_counter_feature_enum.py.-->
   <int value="3726" label="V8HTMLDialogElement_ShowModal_Method"/>
   <int value="3727" label="AdFrameDetected"/>
   <int value="3728" label="MediaStreamTrackGenerator"/>
+  <int value="3729" label="MediaStreamTrackProcessor"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">