Clean up histogram'd media enum max values.

media/base/audio_decoder_config.h

Index: media/base/audio_decoder_config.h
diff --git a/media/base/audio_decoder_config.h b/media/base/audio_decoder_config.h
index 77d4fc28ade49e4b77c8de3c3a3cca93686824a5..3d00de93ae9d6a0e40d65e9e10c74ab221d4f211 100644
--- a/media/base/audio_decoder_config.h
+++ b/media/base/audio_decoder_config.h
@@ -18,7 +18,8 @@ namespace media {
 enum AudioCodec {
   // These values are histogrammed over time; do not change their ordinal
   // values.  When deleting a codec replace it with a dummy value; when adding a
-  // codec, do so at the bottom before kAudioCodecMax.
+  // codec, do so at the bottom before kAudioCodecMax, and update the value of
+  // kAudioCodecMax to equal the new codec.
   kUnknownAudioCodec = 0,
   kCodecAAC = 1,
   kCodecMP3 = 2,
@@ -39,8 +40,8 @@ enum AudioCodec {
   // The only acceptable time to add a new codec is if there is production code
   // that uses said codec in the same CL.
 
-  // Must always be last!
-  kAudioCodecMax
+  // Must always be equal to the last entry!
+  kAudioCodecMax = kCodecPCM_ALAW,
 };
 
 // TODO(dalecurtis): FFmpeg API uses |bytes_per_channel| instead of