Autoplay: add Feature/Runtime flags to turn on/off restrictions on Web Audio.

This is adding a flag to be able to control whether Web Audio should be
restricted by autoplay. It will allow testing and experimenting.

Bug: 841933
Change-Id: Icdec2e74b210f0cf49db87f79ac9a1cb60d94d63
Reviewed-on: https://chromium-review.googlesource.com/1067148Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560350}

content/child/runtime_features.cc

@@ -452,6 +452,9 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
     WebRuntimeFeatures::EnableOriginTrialControlledFeatures(false);
   }
 
+  WebRuntimeFeatures::EnableAutoplayIgnoresWebAudio(
+      base::FeatureList::IsEnabled(media::kAutoplayIgnoreWebAudio));
+
   // Enable explicitly enabled features, and then disable explicitly disabled
   // ones.
   for (const std::string& feature :

media/base/media_switches.cc

@@ -320,6 +320,12 @@ const base::Feature kLowDelayVideoRenderingOnLiveStream{
     "low-delay-video-rendering-on-live-stream",
     base::FEATURE_ENABLED_BY_DEFAULT};
 
+// Whether the autoplay policy should ignore Web Audio. When ignored, the
+// autoplay policy will be hardcoded to be the legacy one on based on the
+// platform
+const base::Feature kAutoplayIgnoreWebAudio{"AutoplayIgnoreWebAudio",
+                                            base::FEATURE_ENABLED_BY_DEFAULT};
+
 #if defined(OS_ANDROID)
 // Lock the screen orientation when a video goes fullscreen.
 const base::Feature kVideoFullscreenOrientationLock{

media/base/media_switches.h

@@ -104,6 +104,7 @@ namespace media {
 // All features in alphabetical order. The features should be documented
 // alongside the definition of their values in the .cc file.
 
+MEDIA_EXPORT extern const base::Feature kAutoplayIgnoreWebAudio;
 MEDIA_EXPORT extern const base::Feature kAv1Decoder;
 MEDIA_EXPORT extern const base::Feature kBackgroundVideoPauseOptimization;
 MEDIA_EXPORT extern const base::Feature kBackgroundVideoTrackOptimization;

third_party/blink/public/platform/web_runtime_features.h

@@ -191,6 +191,7 @@ class WebRuntimeFeatures {
   BLINK_PLATFORM_EXPORT static void EnableOffMainThreadWebSocket(bool);
   BLINK_PLATFORM_EXPORT static void EnableExperimentalProductivityFeatures(
       bool);
+  BLINK_PLATFORM_EXPORT static void EnableAutoplayIgnoresWebAudio(bool);
 
  private:
   WebRuntimeFeatures();

third_party/blink/renderer/modules/webaudio/base_audio_context.cc

@@ -684,13 +684,19 @@ Document* BaseAudioContext::GetDocument() const {
 }
 
 AutoplayPolicy::Type BaseAudioContext::GetAutoplayPolicy() const {
-// The policy is different on Android compared to Desktop.
+  if (RuntimeEnabledFeatures::AutoplayIgnoresWebAudioEnabled()) {
+// When ignored, the policy is different on Android compared to Desktop.
 #if defined(OS_ANDROID)
     return AutoplayPolicy::Type::kUserGestureRequired;
 #else
     // Force no user gesture required on desktop.
     return AutoplayPolicy::Type::kNoUserGestureRequired;
 #endif
+  }
+
+  Document* document = GetDocument();
+  DCHECK(document);
+  return AutoplayPolicy::GetAutoplayPolicyForDocument(*document);
 }
 
 bool BaseAudioContext::AreAutoplayRequirementsFulfilled() const {

third_party/blink/renderer/platform/exported/web_runtime_features.cc

@@ -520,4 +520,8 @@ void WebRuntimeFeatures::EnableDisplayCutoutViewportFit(bool enable) {
   RuntimeEnabledFeatures::SetDisplayCutoutViewportFitEnabled(enable);
 }
 
+void WebRuntimeFeatures::EnableAutoplayIgnoresWebAudio(bool enable) {
+  RuntimeEnabledFeatures::SetAutoplayIgnoresWebAudioEnabled(enable);
+}
+
 }  // namespace blink

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -112,6 +112,10 @@
       name: "AutomationControlled",
       settable_from_internals: true,
     },
+    {
+      // Flag set by the media::kAutoplayIgnoreWebAudio feature flag.
+      name: "AutoplayIgnoresWebAudio",
+    },
     {
       name: "AutoplayMutedVideos",
       settable_from_internals: true,