Add VideoRotation UMA Logging

content/renderer/media/webmediaplayer_impl.cc

Index: content/renderer/media/webmediaplayer_impl.cc
diff --git a/content/renderer/media/webmediaplayer_impl.cc b/content/renderer/media/webmediaplayer_impl.cc
index a6b0fd96e7ed66b2a6f31b8691fa009709662e88..dccea32354f36909709cf5706ef07c73837b33ee 100644
--- a/content/renderer/media/webmediaplayer_impl.cc
+++ b/content/renderer/media/webmediaplayer_impl.cc
@@ -963,6 +963,9 @@ void WebMediaPlayerImpl::OnPipelineMetadata(
 
   pipeline_metadata_ = metadata;
 
+  UMA_HISTOGRAM_ENUMERATION("Media.VideoRotation",
+                            metadata.video_rotation,
+                            media::VIDEO_ROTATION_MAX + 1);

[Alexei Svitkine (slow), 2014/07/17 18:20:59]

Optional nit:

General convention for UMA histograms is to have the MAX entry be 1 higher than
the last entry, so that the +1 here would be unnecessary (once you update the
enum) and also makes it so you don't need to change what the MAX ='s to each
time you add a new entry.

[scherkus (not reviewing), 2014/07/17 18:51:48]

Us media folk decided a while back that defining _MAX as LAST_VALUE + 1 isn't
technically correct as "max" is typically defined as an inclusive endpoint.
Using something like _NUM (which typically is LAST_VALUE + 1) isn't good either
since over the long run, enum values can get deprecated leaving holes in the
enum, leading to _NUM being misleading. Also, introducing an extra enum for the
sake of UMA pollutes all non-UMA switch/case statements.

So we standardized on _MAX and wrote a PRESUBMIT.py to verify that enums, _MAX,
and UMA usage is correct:
http://src.chromium.org/viewvc/chrome/trunk/src/media/PRESUBMIT.py

   SetReadyState(WebMediaPlayer::ReadyStateHaveMetadata);
 
   if (hasVideo()) {