Add UMA stats for SharedWorker in RenderProcessHostImpl.

This cl adds one UMA stats.
- SharedWorker.RendererSurviveForWorkerTime

BUG=327256

Review URL: https://codereview.chromium.org/212403002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@260376 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed