Replace AudioSilenceDetector with an AudioPowerMonitor.

chrome/browser/media/audio_stream_indicator.cc

Index: chrome/browser/media/audio_stream_indicator.cc
diff --git a/chrome/browser/media/audio_stream_indicator.cc b/chrome/browser/media/audio_stream_indicator.cc
index 6cd623212e72fcf8dcc722241af868ec291d5755..a66f8d936107c1baa9b4535b0170475527d80929 100644
--- a/chrome/browser/media/audio_stream_indicator.cc
+++ b/chrome/browser/media/audio_stream_indicator.cc
@@ -4,6 +4,8 @@
 
 #include "chrome/browser/media/audio_stream_indicator.h"
 
+#include <limits>
+
 #include "base/bind.h"
 #include "chrome/browser/tab_contents/tab_util.h"
 #include "content/public/browser/browser_thread.h"
@@ -20,22 +22,66 @@ AudioStreamIndicator::~AudioStreamIndicator() {}
 
 void AudioStreamIndicator::UpdateWebContentsStatus(
     int render_process_id, int render_view_id, int stream_id,
-    bool is_playing_and_audible) {
+    bool is_playing, float power_dBFS, bool clipped) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
       base::Bind(&AudioStreamIndicator::UpdateWebContentsStatusOnUIThread, this,
                  render_process_id, render_view_id, stream_id,
-                 is_playing_and_audible));
+                 is_playing, power_dBFS, clipped));
 }
 
-bool AudioStreamIndicator::IsPlayingAudio(WebContents* contents) {
+bool AudioStreamIndicator::IsPlayingAudio(const WebContents* contents) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  // TODO(miu): In order to prevent breaking existing uses of this method, the
+  // old semantics of "playing AND not silent" have been retained here.  Once
+  // the tab audio indicator UI switches over to using the new
+  // GetAudioSignalPower(), this method should really be just "playing."
+  float level;
+  bool ignored;
+  CurrentAudibleLevel(contents, &level, &ignored);
+  return level > 0.0f;
+}
+
+void AudioStreamIndicator::CurrentAudibleLevel(
+    const content::WebContents* contents, float* level, bool* clipped) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  float max_power_dBFS = -std::numeric_limits<float>::infinity();
+  bool has_clipped = false;
 
-  RenderViewId id(contents->GetRenderProcessHost()->GetID(),
-                  contents->GetRenderViewHost()->GetRoutingID());
-  return audio_streams_.find(id) != audio_streams_.end();
+  // Since a RenderView can have more than one stream playing back, return the
+  // maximum of the last-reported power levels.  For more information about how
+  // the power level is measured, see media/audio/audio_power_monitor.h.
+  const RenderViewId id(contents->GetRenderProcessHost()->GetID(),
+                        contents->GetRenderViewHost()->GetRoutingID());
+  RenderViewStreamMap::iterator stream_it = audio_streams_.find(id);
+  if (stream_it != audio_streams_.end()) {
+    StreamPowerLevelMap& power_levels = stream_it->second;
+    for (StreamPowerLevelMap::iterator power_it = power_levels.begin();
+         power_it != power_levels.end(); ++power_it) {
+      SignalPower& stream_power = power_it->second;
+      if (stream_power.power_dBFS > max_power_dBFS)
+        max_power_dBFS = stream_power.power_dBFS;
+      if (stream_power.clipped) {
+        has_clipped = true;
+        // Clear the flag now that we'll be reporting the clipping.
+        stream_power.clipped = false;
+      }
+    }
+  }
+
+  // Map the power into an "audible level" in the range [0.0,1.0].  dBFS values
+  // are in the range -inf (minimum power) to 0.0 (maximum power).
+  static const float kSilenceThresholdDBFS = -72.24719896f;
+  if (max_power_dBFS < kSilenceThresholdDBFS)
+    *level = 0.0f;
+  else if (max_power_dBFS > 0.0f)
+    *level = 1.0f;
+  else
+    *level = 1.0f - max_power_dBFS / kSilenceThresholdDBFS;
+  *clipped = has_clipped;
 }
 
 AudioStreamIndicator::RenderViewId::RenderViewId(int render_process_id,
@@ -53,23 +99,25 @@ bool AudioStreamIndicator::RenderViewId::operator<(
 }
 
 void AudioStreamIndicator::UpdateWebContentsStatusOnUIThread(
-    int render_process_id,
-    int render_view_id,
-    int stream_id,
-    bool is_playing_and_audible) {
+    int render_process_id, int render_view_id, int stream_id,
+    bool is_playing, float power_dBFS, bool clipped) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  RenderViewId id(render_process_id, render_view_id);
-  if (is_playing_and_audible) {
-    audio_streams_[id].insert(stream_id);
+  const RenderViewId id(render_process_id, render_view_id);
+  if (is_playing) {
+    SignalPower& stream_power = audio_streams_[id][stream_id];
+    stream_power.power_dBFS = power_dBFS;
+    stream_power.clipped |= clipped;
   } else {
-    std::map<RenderViewId, std::set<int> >::iterator it =
-        audio_streams_.find(id);
-    if (it == audio_streams_.end())
+    RenderViewStreamMap::iterator stream_it = audio_streams_.find(id);
+    if (stream_it == audio_streams_.end())
       return;
-
-    it->second.erase(stream_id);
-    if (it->second.empty())
-      audio_streams_.erase(it);
+    StreamPowerLevelMap& power_levels = stream_it->second;
+    StreamPowerLevelMap::iterator power_it = power_levels.find(stream_id);
+    if (power_it == power_levels.end())
+      return;
+    power_levels.erase(power_it);
+    if (power_levels.empty())
+      audio_streams_.erase(stream_it);
   }
 
   WebContents* web_contents = tab_util::GetWebContentsByID(render_process_id,