Track performance of toBlob and its complete timeout delay

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 f670feb2cc201041ee526132224d7bf42636721b..8cf2ea9c095b08fdae7fce43dfb510e1e82484ba 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3579,6 +3579,46 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Time spent on 2D canvas putImageData API call.</summary>
 </histogram>
 
+<histogram name="Blink.Canvas.ToBlob.IdleEncodeDuration" units="microseconds">
+  <owner>junov@chromium.org</owner>
+  <owner>xlai@chromium.org</owner>
+  <summary>
+    This metric measures the total time spent on encoding an image (jpeg or
+    png), as part of canvas.toBlob API call, which occurs during one or more
+    idle periods on the main thread.
+
+    This metric is useful in helping us tuning the parameter
+    IdleTaskCompleteTimeoutDelay in canvas.toBlob.

[xidachen, 2016/06/30 15:25:04]

histogram owners: could you please proof read the description here? Both me and
xlai@ are not sure whether this is too long or not.

+  </summary>
+</histogram>
+
+<histogram name="Blink.Canvas.ToBlob.IdleTaskStatus" enum="IdleTaskStatus">
+  <owner>junov@chromium.org</owner>
+  <owner>xlai@chromium.org</owner>
+  <summary>
+    Records the status of the idle task when finishing a toBlob call.
+  </summary>
+</histogram>
+
+<histogram name="Blink.Canvas.ToBlob.InitiateEncodingDelay"
+    units="microseconds">
+  <owner>junov@chromium.org</owner>
+  <owner>xlai@chromium.org</owner>
+  <summary>
+    This metric measures the time an idle encoding task for canvas.toBlob spends
+    queued before it begins to execute.
+
+    This metric is useful in helping us tuning the parameter
+    IdleTaskStartTimeoutDelay in canvas.toBlob.

[xidachen, 2016/06/30 15:25:04]

histogram owners: please proof read the description here too. Thank you.

+  </summary>
+</histogram>
+
+<histogram name="Blink.Canvas.ToBlobDuration" units="microseconds">
+  <owner>junov@chromium.org</owner>
+  <owner>xlai@chromium.org</owner>
+  <summary>Time spent on 2D canvas toBlob API call.</summary>
+</histogram>
+
 <histogram name="Blink.Canvas.ToDataURL" units="microseconds">
   <owner>junov@chromium.org</owner>
   <summary>Time spent on 2D canvas toDataURL API call.</summary>
@@ -78766,6 +78806,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </int>
 </enum>
 
+<enum name="IdleTaskStatus" type="int">
+  <int value="0" label="IdleTaskNotStarted"/>
+  <int value="1" label="IdleTaskStarted"/>
+  <int value="2" label="IdleTaskCompleted"/>
+  <int value="3" label="IdleTaskFailed"/>
+  <int value="4" label="IdleTaskSwitchedToMainThreadTask"/>
+  <int value="5" label="IdleTaskNotSupported"/>
+</enum>
+
 <enum name="IMECommitType" type="int">
   <obsolete>
     Deprecated 03/2015, and replaced by IMECommitType2.
@@ -93960,6 +94009,20 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Blink.Canvas.PutImageData"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="BlinkCanvasToBlobIdleEncodAndDelayType" separator=".">
+  <suffix name="JPEG"/>
+  <suffix name="PNG"/>
+  <affected-histogram name="Blink.Canvas.ToBlob.IdleEncodeDuration"/>
+  <affected-histogram name="Blink.Canvas.ToBlob.InitiateEncodingDelay"/>
+</histogram_suffixes>
+
+<histogram_suffixes name="BlinkCanvasToBlobType" separator=".">
+  <suffix name="JPEG"/>
+  <suffix name="PNG"/>
+  <suffix name="WEBP"/>
+  <affected-histogram name="Blink.Canvas.ToBlobDuration"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="BlinkCanvasToDataURLTime" separator=".">
   <suffix name="BMP"/>
   <suffix name="GIF"/>