Add a method to tab_utils.h to find out whether a tab is playing audio.

content/browser/renderer_host/media/audio_renderer_host_unittest.cc

Index: content/browser/renderer_host/media/audio_renderer_host_unittest.cc
diff --git a/content/browser/renderer_host/media/audio_renderer_host_unittest.cc b/content/browser/renderer_host/media/audio_renderer_host_unittest.cc
index e8bd79c9d28e3aa48135e9bf43b3bbae6c56e962..b12a02cd2c91fff038033eacaa3b40b881bc4b4b 100644
--- a/content/browser/renderer_host/media/audio_renderer_host_unittest.cc
+++ b/content/browser/renderer_host/media/audio_renderer_host_unittest.cc
@@ -32,6 +32,8 @@ namespace content {
 
 static const int kStreamId = 50;
 
+static const int kRenderProcessId = 42;
+
 static bool IsRunningHeadless() {
   scoped_ptr<base::Environment> env(base::Environment::Create());
   if (env->HasVar("CHROME_HEADLESS"))
@@ -44,7 +46,7 @@ class MockAudioRendererHost : public AudioRendererHost {
   explicit MockAudioRendererHost(
       media::AudioManager* audio_manager,
       MediaObserver* media_observer)
-      : AudioRendererHost(audio_manager, media_observer),
+      : AudioRendererHost(kRenderProcessId, audio_manager, media_observer),
         shared_memory_length_(0) {
   }
 
@@ -222,7 +224,8 @@ class AudioRendererHostTest : public testing::Test {
 
   void Play() {
     EXPECT_CALL(*observer_,
-                OnSetAudioStreamPlaying(_, kStreamId, true));
+                OnSetAudioStreamPlaying(_, kStreamId, kRenderProcessId, 0,
+                                        true));
     EXPECT_CALL(*host_, OnStreamPlaying(kStreamId))
         .WillOnce(QuitMessageLoop(message_loop_.get()));
 
@@ -232,7 +235,8 @@ class AudioRendererHostTest : public testing::Test {
 
   void Pause() {
     EXPECT_CALL(*observer_,
-                OnSetAudioStreamPlaying(_, kStreamId, false));
+                OnSetAudioStreamPlaying(_, kStreamId, kRenderProcessId, 0,
+                                        false));
     EXPECT_CALL(*host_, OnStreamPaused(kStreamId))
         .WillOnce(QuitMessageLoop(message_loop_.get()));