Revert of Gardening: Revert "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/content/browser/media/audio_stream_monitor.h b/content/browser/media/audio_stream_monitor.h
new file mode 100644
index 0000000000000000000000000000000000000000..d1a32d5f857b05925f884ef64d834e673c8c5f29
--- /dev/null
+++ b/content/browser/media/audio_stream_monitor.h
@@ -0,0 +1,153 @@
+// Copyright 2014 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 CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
+#define CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
+
+#include <map>
+#include <utility>
+
+#include "base/callback_forward.h"
+#include "base/threading/thread_checker.h"
+#include "base/time/default_tick_clock.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+#include "build/build_config.h"
+#include "content/common/content_export.h"
+#include "media/audio/audio_output_controller.h"
+
+namespace base {
+class TickClock;
+}
+
+namespace content {
+class WebContents;
+
+// 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
+// when sound is audible; and 2) Hold on for X amount of time after sound has
+// gone silent, then turn off.  Said another way, we don't want tab indicators
+// to turn on/off repeatedly and annoy the user.  AudioStreamMonitor sends UI
+// update notifications only when needed, but may be queried at any time.
+//
+// Each WebContentsImpl owns an AudioStreamMonitor.
+class CONTENT_EXPORT AudioStreamMonitor {
+ public:
+  explicit AudioStreamMonitor(WebContents* contents);
+  ~AudioStreamMonitor();
+
+  // Indicates if audio stream monitoring is available.  It's only available if
+  // AudioOutputController can and will monitor output power levels.
+  static bool monitoring_available() {
+    return media::AudioOutputController::will_monitor_audio_levels();
+  }
+
+  // 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
+  // other use cases as well (e.g., the OOM killer uses this to de-prioritize
+  // the killing of tabs making sounds).
+  bool WasRecentlyAudible() const;
+
+  // 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).  |stream_id| must be unique within a |render_process_id|.
+  typedef base::Callback<std::pair<float, bool>()> ReadPowerAndClipCallback;
+  static void StartMonitoringStream(
+      int render_process_id,
+      int render_frame_id,
+      int stream_id,
+      const ReadPowerAndClipCallback& read_power_callback);
+  static void StopMonitoringStream(int render_process_id,
+                                   int render_frame_id,
+                                   int stream_id);
+
+  void set_was_recently_audible_for_testing(bool value) {
+    was_recently_audible_ = value;
+  }
+
+ private:
+  friend class AudioStreamMonitorTest;
+
+  enum {
+    // Desired polling frequency.  Note: If this is set too low, short-duration
+    // "blip" sounds won't be detected.  http://crbug.com/339133#c4
+    kPowerMeasurementsPerSecond = 15,
+
+    // Amount of time to hold a tab indicator on after its last blurt.
+    kHoldOnMilliseconds = 2000
+  };
+
+  // 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 render_process_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);
+
+  // Called by |poll_timer_| to sample the power levels from each of the streams
+  // playing in the tab.
+  void Poll();
+
+  // Compares last known indicator state with what it should be, and triggers UI
+  // updates through |web_contents_| if needed.  When the indicator is turned
+  // on, |off_timer_| is started to re-invoke this method in the future.
+  void MaybeToggle();
+
+  // The WebContents instance instance to receive indicator toggle
+  // notifications.  This pointer should be valid for the lifetime of
+  // AudioStreamMonitor.
+  WebContents* const web_contents_;
+
+  // Note: |clock_| is always |&default_tick_clock_|, except during unit
+  // testing.
+  base::DefaultTickClock default_tick_clock_;
+  base::TickClock* const clock_;
+
+  // Confirms single-threaded access in debug builds.
+  base::ThreadChecker thread_checker_;
+
+  // The callbacks to read power levels for each stream.  Only playing (i.e.,
+  // not paused) streams will have an entry in this map.
+  typedef std::pair<int, int> StreamID;
+  typedef std::map<StreamID, ReadPowerAndClipCallback> StreamPollCallbackMap;
+  StreamPollCallbackMap poll_callbacks_;
+
+  // Records the last time at which sound was audible from any stream.
+  base::TimeTicks last_blurt_time_;
+
+  // Set to true if the last call to MaybeToggle() determined the indicator
+  // should be turned on.
+  bool was_recently_audible_;
+
+  // Calls Poll() at regular intervals while |poll_callbacks_| is non-empty.
+  base::RepeatingTimer<AudioStreamMonitor> poll_timer_;
+
+  // Started only when an indicator is toggled on, to turn it off again in the
+  // future.
+  base::OneShotTimer<AudioStreamMonitor> off_timer_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_