Move the Ash NPAPI plugin blocker logic

To RenderviewCreated, so in theory there we can
catch cases that we are missing, because we have a crash
which is trying to reparent an NPAPI plugin in metro
ash which should not be happening (should be blocked).

BUG=315565
TEST=see bug
R=jam@chromium.org

Review URL: https://codereview.chromium.org/62373004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233455 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233455