Web Audio: fix two bugs in audibility detection in BaseAudioContext.

Fixing the following issues:
 - take into account AudioContext stopping;
 - removes 10 seconds limitation.

Bug: 897451
Change-Id: I63b22fc20ded193cd032e30722ab35571adba56c
Reviewed-on: https://chromium-review.googlesource.com/c/1292378
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601415}

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

@@ -77,10 +77,6 @@
 
 namespace blink {
 
-// Recording of audio audibility stops after the context has been running for
-// this long.  We don't need this information for the lifetime of the context.
-const double kStopRecordingAudibilityTime = 10;
-
 BaseAudioContext* BaseAudioContext::Create(
     Document& document,
     const AudioContextOptions& context_options,
@@ -605,6 +601,16 @@ void BaseAudioContext::SetContextState(AudioContextState new_state) {
 
   context_state_ = new_state;
 
+  // Audibility checks only happen when the context is running so manual
+  // notification is required when the context gets suspended or closed.
+  if (was_audible_ && context_state_ != kRunning) {
+    was_audible_ = false;
+    PostCrossThreadTask(
+        *task_runner_, FROM_HERE,
+        CrossThreadBind(&BaseAudioContext::NotifyAudibleAudioStopped,
+                        WrapCrossThreadPersistent(this)));
+  }
+
   // Notify context that state changed
   if (GetExecutionContext()) {
     GetExecutionContext()
@@ -721,14 +727,10 @@ void BaseAudioContext::HandlePostRenderTasks(const AudioBus* destination_bus) {
     // Detect silence (or not) for MEI
     bool is_audible = IsAudible(destination_bus);
 
-    // We want to keep track of the total audible audio, but we don't need to
-    // record the start and stop of audible audio after
-    // |kStopRecordingAudibilityTime|.
     if (is_audible) {
       ++total_audible_renders_;
     }
 
-    if (currentTime() <= kStopRecordingAudibilityTime) {
     if (was_audible_ != is_audible) {
       // Audibility changed in this render, so report the change.
       was_audible_ = is_audible;
@@ -745,7 +747,6 @@ void BaseAudioContext::HandlePostRenderTasks(const AudioBus* destination_bus) {
       }
     }
   }
-  }
 }
 
 void BaseAudioContext::PerformCleanupOnMainThread() {