Clean up histogram'd media enum max values.

media/audio/sample_rates.h

Index: media/audio/sample_rates.h
diff --git a/media/audio/sample_rates.h b/media/audio/sample_rates.h
index 7c29e548b340e385512eedf82821a0f9f15f7060..482ec0fdc8b2fcbbe25d3b46e58058fd25ca2a7d 100644
--- a/media/audio/sample_rates.h
+++ b/media/audio/sample_rates.h
@@ -23,12 +23,13 @@ enum AudioSampleRate {
   k88200Hz = 8,
   k176400Hz = 9,
   k192000Hz = 10,
-  kUnexpectedAudioSampleRate  // Must always be last!
+  // Must always equal the largest value ever reported:
+  kAudioSampleRateMax = k192000Hz,
 };
 
 // Helper method to convert integral values to their respective enum values,
-// or kUnexpectedAudioSampleRate if no match exists.
-MEDIA_EXPORT AudioSampleRate AsAudioSampleRate(int sample_rate);
+// returns false for unexpected sample rates.
+MEDIA_EXPORT bool ToAudioSampleRate(int sample_rate, AudioSampleRate* asr);
 
 }  // namespace media