Add in support for internal pepper plugins into the PepperPluginRegistry and pepper::PluginModule.

Used Chromoting's plugin as the first attempt at using this interface.

BUG=none
TEST=compiles

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=50667

Review URL: http://codereview.chromium.org/2843018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@50976 0039d316-1c4b-4281-b951-d872f2087c98