[AudioStreamMonitor] Adds API to collect frame-level audibility.

content/browser/media/audio_stream_monitor.h

Index: content/browser/media/audio_stream_monitor.h
diff --git a/content/browser/media/audio_stream_monitor.h b/content/browser/media/audio_stream_monitor.h
index f925c91ebe13af336480b91c1ad01c43faabb37f..bed4d362d0d376d34a23910232a3bdf551e6eef1 100644
--- a/content/browser/media/audio_stream_monitor.h
+++ b/content/browser/media/audio_stream_monitor.h
@@ -14,6 +14,7 @@
 #include "base/time/default_tick_clock.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
+#include "base/tuple.h"
 #include "build/build_config.h"
 #include "content/common/content_export.h"
 #include "media/audio/audio_output_controller.h"
@@ -111,12 +112,15 @@ class CONTENT_EXPORT AudioStreamMonitor {
   // Starts polling the stream for audio stream power levels using |callback|.
   void StartMonitoringStreamOnUIThread(
       int render_process_id,
+      int render_frame_id,
       int stream_id,
       const ReadPowerAndClipCallback& callback);
 
   // Stops polling the stream, discarding the internal copy of the |callback|
   // provided in the call to StartMonitoringStream().
-  void StopMonitoringStreamOnUIThread(int render_process_id, int stream_id);
+  void StopMonitoringStreamOnUIThread(int render_process_id,
+                                      int render_frame_id,
+                                      int stream_id);
 
   // Called by |poll_timer_| to sample the power levels from each of the streams
   // playing in the tab.
@@ -146,7 +150,8 @@ class CONTENT_EXPORT AudioStreamMonitor {
 
   // The callbacks to read power levels for each stream.  Only playing (i.e.,
   // not paused) streams will have an entry in this map.
-  using StreamID = std::pair<int, int>;
+  // StreamID is formed by <render_process_id, render_frame_id, stream_id>
+  using StreamID = std::tuple<int, int, int>;

[DaleCurtis, 2017/06/22 00:35:55]

This would be clearer as:

struct StreamID {
  int render_process_id;
  int render_frame_id;
  int stream_id;
};

You'll still be able to initialize it the same way (as POD type you can use =
{1,2,3}), but now we have named fields for legibility.

[lpy, 2017/06/22 02:28:52]

Done.

   using StreamPollCallbackMap = std::map<StreamID, ReadPowerAndClipCallback>;
   StreamPollCallbackMap poll_callbacks_;