publish canvas context API stat metrics

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 9d6c163acca5807d32a8c319d7c52d73e7822f0c..0904d1ac18315bb6ec0182d306fdb79408161c56 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -51281,6 +51281,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebCore.CanvasContextStat" enum="CanvasContextStat">
+  <owner>zmin@chromium.org</owner>

[Justin Novosad, 2015/11/20 03:30:44]

Since your team assignment is not set in stone yet, better add my name here,
just in case.

[zmin, 2015/11/20 17:08:33]

Done.

[zmin, 2015/11/20 17:08:33]

Done.

+  <summary>The State of Canvas 2D Context API.</summary>
+</histogram>
+
 <histogram name="WebCore.DistillabilityUs" units="microseconds">
   <owner>wychen@chromium.org</owner>
   <summary>
@@ -55448,6 +55453,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="4" label="CACHE_MISS"/>
 </enum>
 
+<enum name="CanvasContextStat" type="int">
+  <int value="0" label="CanvasCreated"/>
+  <int value="1" label="CanvasContextCreated"/>
+  <int value="2" label="GPUAccelerated2DCanvasImageBufferCreated"/>
+  <int value="3" label="DisplayList2DCanvasImageBufferCreated"/>
+  <int value="4" label="Unaccelerated2DCanvasImageBufferCreated"/>
+  <int value="5" label="Accelerated2DCanvasGPUContextLost"/>
+  <int value="6" label="Unaccelerated2DCanvasImageBufferCreationFailed"/>
+  <int value="7" label="GPUAccelerated2DCanvasImageBufferCreationFailed"/>
+  <int value="8" label="DisplayList2DCanvasFallbackToRaster"/>
+</enum>
+
 <enum name="CanvasContextType" type="int">

[Justin Novosad, 2015/11/20 03:30:44]

Looks like someone else had the idea to count context creations, but this does
not appear to be referenced anywhere. I think it should be removed along with
the associated Canvas.ContextType histogram earlier in this file.

[zmin, 2015/11/20 17:08:33]

Talk with @junov offline. We will remove CanvasContextCreated for
CanvasContextStat as it's duplicated with Canvas.ContextType. Also update the
Cnvas.ContextType to match the enum in C++ file.

   <int value="0" label="2d"/>
   <int value="1" label="webkit-3d"/>