cc: Add UMA for tracking decode duration for out of raster decodes.

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 3cb4e1df495072edb9f3a50c9caa48d1d4a48e68..bf86e11704684906d7cfea9bba97448402adb068 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -58701,9 +58701,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram name="Renderer4.ImageDecodeTaskDurationUs" units="microseconds">

[vmpstr, 2017/06/01 21:40:56]

There was some magic with suffixes that I think you can use here. Or maybe this
is OK. I'll defer to histograms owners on this.

[Khushal, 2017/06/01 23:45:09]

Yeah, I don't know how it works with 2 suffixes.

[Ilya Sherman, 2017/06/01 23:50:50]

You can use suffixes recursively, but I think it's fine the way it's written
too.

[Khushal, 2017/06/02 00:17:22]

Acknowledged.

   <owner>vmpstr@chromium.org</owner>
   <summary>
-    This metric records the duration of an image decode in the compositor. It is
-    recorded every time we decode an image. It is suffixed by the type of
-    rasterization we're in (either Gpu or Software).
+    This metric records the duration of an image decode for the raster path in
+    the compositor. It is recorded every time we decode an image. It is suffixed
+    by the type of rasterization we're in (either Gpu or Software).
+  </summary>
+</histogram>
+
+<histogram name="Renderer4.ImageDecodeTaskDurationUs.OutOfRaster"
+    units="microseconds">
+  <owner>vmpstr@chromium.org, khushalsagar@chromium.org</owner>
+  <summary>
+    This metric records the duration of an image decode for out of raster path
+    in the compositor. It is recorded every time we decode an image. It is
+    suffixed by the type of rasterization we're in (either Gpu or Software).
   </summary>
 </histogram>
 
@@ -91215,6 +91225,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
       name="Compositing.Renderer.RasterTask.RasterPixelsPerMs2"/>
   <affected-histogram name="Compositing.Renderer.RasterTask.RasterUs"/>
   <affected-histogram name="Renderer4.ImageDecodeTaskDurationUs"/>
+  <affected-histogram name="Renderer4.ImageDecodeTaskDurationUs.OutOfRaster"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="ReferrerAttribution" separator=".">