Cancel pending changes when navigating away from the NTP.
Cancel pending changes when navigating away from the NTP.

BUG=12426
TEST=From the New Tab Page (NTP), click the Remove thumbnails link, remove thumbnails but don't press the Done button. Navigate to a URL (ex: www.google.com). Navigate to the NTP again, the thumbnails removed previously should still be showing. Also test that removal works properly when pressing the Done button.
Review URL: http://codereview.chromium.org/118119

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@17451 0039d316-1c4b-4281-b951-d872f2087c98

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