Add a histogram to measure task execution time for the render thread.
Add a histogram to measure task execution time for the render thread.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6670029

git-svn-id: http://src.chromium.org/svn/trunk/src@78511 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 919521f68b1cf14c783237c4fc8a3cdc11bcba48
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser