Clean up histogram'd media enum max values.

media/base/sample_format.h

Index: media/base/sample_format.h
diff --git a/media/base/sample_format.h b/media/base/sample_format.h
index 3d2799fa1287e54b6827c3c95be5573daad0ab3c..7c3df702157dc0f0f43e5422e5f9fde94e007c68 100644
--- a/media/base/sample_format.h
+++ b/media/base/sample_format.h
@@ -12,7 +12,8 @@ namespace media {
 enum SampleFormat {
   // These values are histogrammed over time; do not change their ordinal
   // values.  When deleting a sample format replace it with a dummy value; when
-  // adding a sample format, do so at the bottom before kSampleFormatMax.
+  // adding a sample format, do so at the bottom before kSampleFormatMax, and
+  // update the value of kSampleFormatMax.
   kUnknownSampleFormat = 0,
   kSampleFormatU8,         // Unsigned 8-bit w/ bias of 128.
   kSampleFormatS16,        // Signed 16-bit.
@@ -21,8 +22,8 @@ enum SampleFormat {
   kSampleFormatPlanarS16,  // Signed 16-bit planar.
   kSampleFormatPlanarF32,  // Float 32-bit planar.
 
-  // Must always be last!
-  kSampleFormatMax
+  // Must always be equal to largest value ever logged.
+  kSampleFormatMax = kSampleFormatPlanarF32,
 };
 
 // Returns the number of bytes used per channel for the specified