Reland r100733 - Cancel plugin channel requests when the renderer goes away.

Logic:
- Profile shutdown kills all renderer processes
- When the RMF detects the channel closing, it kills off any plugin channel requests from:
* PluginService (which needs to check the PluginServiceFilter on the FILE thread)
* PluginProcessHost (which may need to wait for the channel to get established)
- RMF uses the new OnPluginProcessHostFound() to cancel at the PluginService or PluginProcessHost

Modified in Reland:
* PluginProcessHost may be blocked on the browser<=>plugin channel to be established, OR on the plugin<=>renderer channel to be established.
* Already covered the former case in the previous changelist (pending_requests_) but not the latter case (sent_requests_).
* Cover both cases and add tests.

BUG=94704
TEST=New PluginService tests

Review URL: http://codereview.chromium.org/7887027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@101181 0039d316-1c4b-4281-b951-d872f2087c98
9 files changed