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..2d9b6e44fbc9721cba4e67b095d2e0835a77f93f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3478,7 +3478,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="Canvas.ContextType" enum="CanvasContextType">
-  <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
+  <owner>junov@chromium.org</owner>
+  <owner>kbr@chromium.org</owner>
   <summary>
     Records the context type names used to create canvas rendering contexts.
   </summary>
@@ -51281,6 +51282,12 @@ 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>
+  <owner>junov@chromium.org</owner>
+  <summary>The State of Canvas 2D Context API.</summary>
+</histogram>
+
 <histogram name="WebCore.DistillabilityUs" units="microseconds">
   <owner>wychen@chromium.org</owner>
   <summary>
@@ -55448,11 +55455,22 @@ 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="GPUAccelerated2DCanvasImageBufferCreated"/>
+  <int value="2" label="DisplayList2DCanvasImageBufferCreated"/>
+  <int value="3" label="Unaccelerated2DCanvasImageBufferCreated"/>
+  <int value="4" label="Accelerated2DCanvasGPUContextLost"/>
+  <int value="5" label="Unaccelerated2DCanvasImageBufferCreationFailed"/>
+  <int value="6" label="GPUAccelerated2DCanvasImageBufferCreationFailed"/>
+  <int value="7" label="DisplayList2DCanvasFallbackToRaster"/>
+</enum>
+
 <enum name="CanvasContextType" type="int">
   <int value="0" label="2d"/>
-  <int value="1" label="webkit-3d"/>

[Justin Novosad, 2015/11/20 17:30:27]

I'm not sure we should remove this even though it is no longer used. We may have
historical data that references this value. Deferring to rkaplow who knows more
about how this stuff works.

   <int value="2" label="experimental-webgl"/>
   <int value="3" label="webgl"/>
+  <int value="4" label="webgl2"/>
 </enum>
 
 <enum name="CAPSUpdaterStep" type="int">