Use AudioStreamMonitor to control power save blocking.

content/browser/media/audio_stream_monitor.h

Index: content/browser/media/audio_stream_monitor.h
diff --git a/chrome/browser/media/audio_stream_monitor.h b/content/browser/media/audio_stream_monitor.h
similarity index 65%
rename from chrome/browser/media/audio_stream_monitor.h
rename to content/browser/media/audio_stream_monitor.h
index 3282dbd8ba77edde54c6c35afb17bd4f49e5068e..2f8f05bb9c735d7a9a11d83bc252561eb83135c0 100644
--- a/chrome/browser/media/audio_stream_monitor.h
+++ b/content/browser/media/audio_stream_monitor.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CHROME_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
-#define CHROME_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
+#ifndef CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
+#define CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
 
 #include <map>
 
@@ -18,6 +18,9 @@ namespace base {
 class TickClock;
 }
 
+namespace content {
+class PowerSaveBlocker;
+
 // Repeatedly polls audio streams for their power levels, and "debounces" the
 // information into a simple, binary "was recently audible" result for the audio
 // indicators in the tab UI.  The debouncing logic is to: 1) Turn on immediately
@@ -31,8 +34,11 @@ class TickClock;
 // AudioStreamMonitor is created on-demand, and automatically destroyed when its
 // associated WebContents is destroyed.  See content::WebContentsUserData for
 // usage.
-class AudioStreamMonitor
-    : public content::WebContentsUserData<AudioStreamMonitor> {
+//
+// AudioStreamMonitor will additionally create a PowerSaveBlocker to prevent app
+// suspension when audible audio is being produced.
+class CONTENT_EXPORT AudioStreamMonitor
+    : public WebContentsUserData<AudioStreamMonitor> {
  public:
   // Returns true if audio has recently been audible from the tab.  This is
   // usually called whenever the tab data model is refreshed; but there are
@@ -40,17 +46,24 @@ class AudioStreamMonitor
   // the killing of tabs making sounds).
   bool WasRecentlyAudible() const;
 
-  // Starts polling the stream for audio stream power levels using |callback|.
+  // Starts or stops audio level monitoring respectively for the stream owned by
+  // the specified renderer.  Safe to call from any thread.
+  //
+  // The callback returns the current power level (in dBFS units) and the clip
+  // status (true if any part of the audio signal has clipped since the last
+  // callback run).
   typedef base::Callback<std::pair<float, bool>()> ReadPowerAndClipCallback;
-  void StartMonitoringStream(int stream_id,
-                             const ReadPowerAndClipCallback& callback);
-
-  // Stops polling the stream, discarding the internal copy of the |callback|
-  // provided in the call to StartMonitoringStream().
-  void StopMonitoringStream(int stream_id);
+  static void StartMonitoringStream(
+      int render_process_id,
+      int render_frame_id,
+      int stream_id,

[miu, 2014/09/02 21:04:39]

This just occurred to me: Are stream_ids unique over an entire browser, or just
inside one render process?  Maybe the internals of ASM need to key by
render_process_id+stream_id, and not just stream_id by itself?

To be clear, if the change is needed, this would be fixing a pre-existing bug.

[DaleCurtis, 2014/09/03 18:48:55]

Yeah, I noticed this too when refactoring and hadn't had a chance to sleuth it
out yet. The stream ids are created from an IDMap owned by AudioMessageFilter
which is in turn owned by the RenderThreadImpl.

My knowledge is a bit out of date on whether RenderThreadImpl ->
RenderProcessHostImpl is a 1:1 mapping. I'd guess not though... miu@, jam@ can
you confirm? If not I'll fix that in a separate patch before landing this one.

[miu, 2014/09/03 22:41:53]

If the stream IDs are created in the render process, there can't be a guarantee
that they will be unique over the whole browser.  Looks like ID map always vends
out integer IDs starting at 1.  So, yep, I'm pretty sure this is a bug that
needs to be fixed.

[DaleCurtis, 2014/09/04 21:59:06]

Fixed, not too hard. Just added a std::pair<int,int> for the map key.

+      const ReadPowerAndClipCallback& read_power_callback);
+  static void StopMonitoringStream(int render_process_id,
+                                   int render_frame_id,
+                                   int stream_id);
 
  private:
-  friend class content::WebContentsUserData<AudioStreamMonitor>;
+  friend class WebContentsUserData<AudioStreamMonitor>;
   friend class AudioStreamMonitorTest;
 
   enum {
@@ -62,10 +75,30 @@ class AudioStreamMonitor
     kHoldOnMilliseconds = 2000
   };
 
-  // Invoked by content::WebContentsUserData only.
-  explicit AudioStreamMonitor(content::WebContents* contents);
+  // Invoked by WebContentsUserData only.
+  explicit AudioStreamMonitor(WebContents* contents);
   virtual ~AudioStreamMonitor();
 
+  // Helper methods for starting and stopping monitoring which lookup the
+  // identified renderer and forward calls to the correct AudioStreamMonitor.
+  static void StartMonitoringHelper(
+      int render_process_id,
+      int render_frame_id,
+      int stream_id,
+      const ReadPowerAndClipCallback& read_power_callback);
+  static void StopMonitoringHelper(int render_process_id,
+                                   int render_frame_id,
+                                   int stream_id);
+
+  // Starts polling the stream for audio stream power levels using |callback|.
+  void StartMonitoringStreamOnUIThread(
+      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 stream_id);
+
   // Called by |poll_timer_| to sample the power levels from each of the streams
   // playing in the tab.
   void Poll();
@@ -78,7 +111,7 @@ class AudioStreamMonitor
   // The WebContents instance instance to receive indicator toggle
   // notifications.  This pointer should be valid for the lifetime of
   // AudioStreamMonitor.
-  content::WebContents* const web_contents_;
+  WebContents* const web_contents_;
 
   // Note: |clock_| is always |&default_tick_clock_|, except during unit
   // testing.
@@ -107,7 +140,12 @@ class AudioStreamMonitor
   // future.
   base::OneShotTimer<AudioStreamMonitor> off_timer_;
 
+  // Prevent app suspension when audio is active.
+  scoped_ptr<PowerSaveBlocker> blocker_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
 };
 
-#endif  // CHROME_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_