The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2c94c4d78f44069ccca52395105f284f51bcf028

commit 2c94c4d78f44069ccca52395105f284f51bcf028
Author: keishi <keishi@chromium.org>
Date: Thu Mar 09 05:13:15 2017

Adds UMA metrics for renderer uptime

Adds UMA metrics for renderer uptime to understand memory usage of long running Chrome.

This adds two metrics:
Memory.Experimental.Renderer.Uptime logs uptime of a render process.
Memory.Experimental.Renderer.LoadsInMainFrameDuringUptime logs the number of main frame page loads that happen in the lifetime of a render process.

BUG=693524

Review-Url: https://codereview.chromium.org/2697323004
Cr-Commit-Position: refs/heads/master@{#455670}

[modify] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/chrome/browser/BUILD.gn
[modify] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/chrome/browser/chrome_browser_main.cc
[add] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/chrome/browser/metrics/renderer_uptime_tracker.cc
[add] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/chrome/browser/metrics/renderer_uptime_tracker.h
[add] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/chrome/browser/metrics/renderer_uptime_web_contents_observer.cc
[add] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/chrome/browser/metrics/renderer_uptime_web_contents_observer.h
[modify] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/chrome/browser/ui/tab_helpers.cc
[modify] https://crrev.com/2c94c4d78f44069ccca52395105f284f51bcf028/tools/metrics/histograms/histograms.xml