Cast: add UMA for video encode accelerator initialization result.

Add Cast.Sender.VideoEncodeAcceleratorInitializeSuccess indicating
whether we were successful in initializing an external video encode
accelerator for cast sender.

BUG=397038
TEST=Cast, check histograms

Review URL: https://codereview.chromium.org/458693004

Cr-Commit-Position: refs/heads/master@{#289029}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289029 0039d316-1c4b-4281-b951-d872f2087c98

media/cast/sender/external_video_encoder.cc

@@ -9,6 +9,7 @@
 #include "base/memory/scoped_vector.h"
 #include "base/memory/shared_memory.h"
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/histogram.h"
 #include "media/base/video_frame.h"
 #include "media/base/video_util.h"
 #include "media/cast/cast_defines.h"
@@ -103,12 +104,16 @@ class LocalVideoEncodeAcceleratorClient
     }
     max_frame_rate_ = video_config.max_frame_rate;
 
-    if (!video_encode_accelerator_->Initialize(
+    bool result = video_encode_accelerator_->Initialize(
         media::VideoFrame::I420,
         gfx::Size(video_config.width, video_config.height),
         output_profile,
         video_config.start_bitrate,
-            this)) {
+        this);
+
+    UMA_HISTOGRAM_BOOLEAN("Cast.Sender.VideoEncodeAcceleratorInitializeSuccess",
+                          result);
+    if (!result) {
       NotifyError(VideoEncodeAccelerator::kInvalidArgumentError);
       return;
     }

tools/metrics/histograms/histograms.xml

@@ -2194,6 +2194,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Cast.Sender.VideoEncodeAcceleratorInitializeSuccess"
+    enum="BooleanSuccess">
+  <owner>posciak@chromium.org</owner>
+  <summary>
+    Indicates whether initialization of a video encode accelerator for Cast
+    sender was successful.
+  </summary>
+</histogram>
+
 <histogram name="Cellular.ActivationFailure">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>