The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e7bad168e3e78aa062b663adea7988552a7978d6

commit e7bad168e3e78aa062b663adea7988552a7978d6
Author: sunyunjia <sunyunjia@chromium.org>
Date: Fri Sep 09 20:22:43 2016

Add UMA for selection drag autoscroll.

BUG= 644741 

Review-Url: https://codereview.chromium.org/2319623004
Cr-Commit-Position: refs/heads/master@{#417689}

[add] https://crrev.com/e7bad168e3e78aa062b663adea7988552a7978d6/third_party/WebKit/LayoutTests/fast/events/drag-and-drop-autoscroll-use-count.html
[modify] https://crrev.com/e7bad168e3e78aa062b663adea7988552a7978d6/third_party/WebKit/Source/core/frame/UseCounter.h
[modify] https://crrev.com/e7bad168e3e78aa062b663adea7988552a7978d6/third_party/WebKit/Source/core/page/AutoscrollController.cpp
[modify] https://crrev.com/e7bad168e3e78aa062b663adea7988552a7978d6/tools/metrics/histograms/histograms.xml