Revert of Change the video color space default.

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 b97ee1b98d3c7a05db7966bf5fb1cc7933da17ef..2588e46e99d96b6dd8156feee0da1450e241ca90 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -62,14 +62,14 @@
     FORMAT_MAX = XRGB,  // Must always be equal to largest entry logged.
   };
 
-  // Color space or color range used for the pixels.
+  // Color space or color range used for the pixels, in general this is left
+  // unspecified, meaning Rec601 (SD) is assumed.
   // Logged to UMA, so never reuse values. Leave gaps if necessary.
   enum ColorSpace {
     COLOR_SPACE_UNSPECIFIED = 0,  // In general this is Rec601.
     COLOR_SPACE_JPEG = 1,  // JPEG color range.
     COLOR_SPACE_HD_REC709 = 2,  // Rec709 "HD" color space.
-    COLOR_SPACE_SD_REC601 = 3,  // Rec601 "SD" color space.
-    COLOR_SPACE_MAX = COLOR_SPACE_SD_REC601,
+    COLOR_SPACE_MAX = COLOR_SPACE_HD_REC709,
   };
 
   // Defines the pixel storage type. Differentiates between directly accessible