Record size of scroller that user scrolls

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 b9111bb3ddfc3f3016e3dcb3737f9482bcee38ae..3d1dc5f37e31d6ba5def29cdebf8b81d45cfaf27 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -16592,6 +16592,28 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Event.Scroll.Touch.ScrollerSize" units="squared pixels">
+  <owner>yigu@chromium.org</owner>
+  <owner>input-dev@chromium.org</owner>
+  <summary>
+    Record the size of a scroller upon ScrollBegin. This is intended to help us
+    measuring the frequencies of different sizes of scrollers getting scrolled.
+    For those small scrollers that users may rarely scroll, there is no need to
+    composite them even we are able to do so.
+  </summary>
+</histogram>
+
+<histogram name="Event.Scroll.Wheel.ScrollerSize" units="squared pixels">
+  <owner>yigu@chromium.org</owner>
+  <owner>input-dev@chromium.org</owner>
+  <summary>
+    Record the size of a scroller upon ScrollBegin. This is intended to help us
+    measuring the frequencies of different sizes of scrollers getting scrolled.
+    For those small scrollers that users may rarely scroll, there is no need to
+    composite them even we are able to do so.

[jwd, 2017/03/27 17:28:34]

Since the summary is basically duplicated, can you redefine these two histograms
using histogram suffixes.

[yigu, 2017/03/27 22:02:15]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Event.SingleTapType" enum="TapDelayType">
   <owner>tdresser@chromium.org</owner>
   <owner>input-dev@chromium.org</owner>