Revert r9861 to fix build

media/audio/audio_output.h

Index: media/audio/audio_output.h
diff --git a/media/audio/audio_output.h b/media/audio/audio_output.h
index 12ef3d9907590dc5716c9472f2ecd35ecbc34102..7d82500fba5317137c6411d6c1c3e97d296f2c9a 100644
--- a/media/audio/audio_output.h
+++ b/media/audio/audio_output.h
@@ -104,11 +104,9 @@ class AudioOutputStream {
 class AudioManager {
  public:
   enum Format {
-    AUDIO_PCM_LINEAR = 0, // Pulse code modulation means 'raw' amplitude
-                          // samples.
-    AUDIO_PCM_DELTA,      // Delta-encoded pulse code modulation.
-    AUDIO_MOCK,           // Creates a dummy AudioOutputStream object.
-    AUDIO_LAST_FORMAT     // Only used for validation of format.
+    AUDIO_PCM_LINEAR,  // Pulse code modulation means 'raw' amplitude samples.
+    AUDIO_PCM_DELTA,   // Delta-encoded pulse code modulation. 
+    AUDIO_MOCK         // Creates a dummy AudioOutputStream object.
   };
 
   // Telephone quality sample rate, mostly for speech-only audio.