Fix a declarativeContent crash on pages with iframes, and make removing rules revert their actions.

BUG=172011

Review URL: https://codereview.chromium.org/25537004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226666 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226666