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 eeea9193acb9d4e9a4283bcdc7b6759c2d6d35be..42f37a99172d2f420bb70bec2ef81b07c01149b3 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3478,6 +3478,11 @@ 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" units="microseconds">
+  <owner>junov@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>
@@ -4336,6 +4341,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Canvas.ToBlob.IdleTaskCompleteTimeoutDelay" enum="MimeType">
+  <owner>xlai@chromium.org</owner>
+  <summary>
+    Records the occurence of complete time out delay in canvas toBlob calls.
+  </summary>
+</histogram>
+
 <histogram name="CAPSUpdater.Step" enum="CAPSUpdaterStep">
   <owner>cpu@chromium.org</owner>
   <summary>
@@ -80730,6 +80742,12 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="2" label="IPsec"/>
 </enum>
 
+<enum name="MimeType" type="int">
+  <int value="0" label="Png"/>
+  <int value="1" label="Jpeg"/>
+  <int value="2" label="Webp"/>
+</enum>
+
 <enum name="MissingStartType" type="int">
   <int value="0" label="Nothing missing"/>
   <int value="1" label="Start missing"/>
@@ -91812,6 +91830,14 @@ 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="BlinkCanvasToBlobTime" separator=".">
+  <suffix name="JPEG"/>
+  <suffix name="PNG"/>
+  <suffix name="Unknown"/>
+  <suffix name="WEBP"/>
+  <affected-histogram name="Blink.Canvas.ToBlob"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="BlinkCanvasToDataURLTime" separator=".">
   <suffix name="BMP"/>
   <suffix name="GIF"/>