Add UMA metrics for ffmpeg color ranges.

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index df383d0d79849a9b746645cdf07febedeceaf461..8deab2db7ce1ed120b8991c59ea8fc33f9967660 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -39,6 +39,7 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // Surface formats roughly based on FOURCC labels, see:
   // http://www.fourcc.org/rgb.php
   // http://www.fourcc.org/yuv.php
+  // Logged to UMA, so never reuse values.
   enum Format {
     INVALID = 0,  // Invalid format value.  Used for error reporting.
     RGB32 = 4,  // 32bpp RGB packed with extra byte 8:8:8
@@ -51,6 +52,7 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
     HOLE = 13,  // Hole frame.
 #endif
     YV12A = 14,  // 20bpp YUVA planar 1x1 Y, 2x2 VU, 1x1 A samples.
+    HISTOGRAM_MAX,  // Must be greater than all other formats.
   };
 
   // Returns the name of a Format as a string.