Remove assertion when destroying a plugin that doesn't exist. The DidDestroy
function will always be called, so the proxy should always add it regardless
of the initialization status.

I also did some clarification of the Destroy path.

BUG=78112
Review URL: http://codereview.chromium.org/6706025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@80336 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed