Implement SharedWorkerServiceImpl::TerminateWorker().

This will be called when the user clicks "terminate" in chrome://inspect/#workers

BUG=327256

Review URL: https://codereview.chromium.org/183663025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255017 0039d316-1c4b-4281-b951-d872f2087c98
Add IncrementWorkerRefCount() and DecrementWorkerRefCount() to RenderProcessHostImpl.

These methods will be called from SharedWorkerServiceImpl when the existence of the other renderer process which is connected to the SharedWorker in this renderer process has changed.
It is only called when "enable-embedded-shared-worker" flag is set.

When |worker_ref_count_| is not zero , RenderProcessHostImpl::FastShutdownIfPossible() and RenderProcessHostImpl::Cleanup() don't shutdown the renderer process.

BUG=327256

Review URL: https://codereview.chromium.org/176843004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255018 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255017
SVN changes up to revision 255018