Remove NOTIFICATION_WEB_CONTENTS_VISIBILITY_CHANGED from autofill.

BUG=170921
TEST=everything still works

Review URL: https://codereview.chromium.org/26553002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227798 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227798
Made the preview auto-cancel used for app print testing more realistic.

Previously this auto-cancel was accomplished directly in C++, causing
print preview dialog cancellations triggerred in tests to behave
slightly differently from similar cancellations initiated by users.
The most notable difference was that test cancellations happened
immediately after the print preview dialog was brought up whereas
user-initiated cancellations only happen on the next pass through the
JavaScript event loop. Differences like these were not a problem for
basic tests but would prevent some more advanced tests that are being
developed from working.

This change lists has auto-cancel work by sending a mouse click event to
the dialog's cancel button, replicating almost exactly what happens for
user-initiated cancellations.

BUG=none

Review URL: https://codereview.chromium.org/26564003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227799 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227799