Add canvas context type histogram

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 fecd8a04c4665a07428dc687595e45e57840bd57..884e3c60c3ee59fbff98f723a68ba9fdcea617b0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1085,6 +1085,12 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Canvas.ContextType" enum="CanvasContextType">
+  <summary>
+    Records the context type names used to create canvas rendering contexts.

[Mark P, 2013/08/02 15:40:58]

for my edification (don't revise the comment):
Is this recorded (in effect) once only when the canvas is created?  Does
scrolling/resizing/etc. cause this to be emitted?

+  </summary>
+</histogram>
+
 <histogram name="Cellular.ActivationFailure">
   <summary>
     The count of cellular device activation failures (Chrome OS).
@@ -15547,6 +15553,13 @@ other types of suffix sets.
   <int value="1" label="Wiped out"/>
 </enum>
 
+<enum name="CanvasContextType" type="int">
+  <int value="0" label="2d"/>
+  <int value="1" label="webkit-3d"/>
+  <int value="2" label="experimental-webgl"/>
+  <int value="3" label="webgl"/>
+</enum>
+
 <enum name="ChannelLayout" type="int">
   <int value="0" label="CHANNEL_LAYOUT_NONE"/>
   <int value="1" label="CHANNEL_LAYOUT_UNSUPPORTED"/>
@@ -20826,6 +20839,12 @@ other types of suffix sets.
   <int value="2" label="Dismiss"/>
 </enum>
 
+<enum name="SimpleCache.FileDescriptorLimitStatus" type="int">
+  <int value="0" label="Unsupported"/>
+  <int value="1" label="Supported but failed"/>
+  <int value="2" label="Succeeded"/>
+</enum>
+
 <enum name="SimpleCacheHeaderSizeChange" type="int">
   <int value="0" label="Written for the first time"/>
   <int value="1" label="Rewritten with same size"/>
@@ -20834,12 +20853,6 @@ other types of suffix sets.
   <int value="4" label="Unexpected header stream write"/>
 </enum>
 
-<enum name="SimpleCache.FileDescriptorLimitStatus" type="int">
-  <int value="0" label="Unsupported"/>
-  <int value="1" label="Supported but failed"/>
-  <int value="2" label="Succeeded"/>
-</enum>
-
 <enum name="SimpleCacheIndexInitializeMethod" type="int">
   <int value="0" label="Directory Scan"/>
   <int value="1" label="Index File"/>