Adds test for cancelling overview mode on click/tap.
Adds test for cancelling overview mode on click/tap.

Adds unittests to verify that clicking/tapping on the desktop iteself while in overview mode causes the user to leave overview mode.

BUG=364507
TEST=WindowSelectorTest.CancelOverviewOnTap, WindowSelectorTest.CancelOverviewOnClick

Review URL: https://codereview.chromium.org/445693004

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@288719 0039d316-1c4b-4281-b951-d872f2087c98

littlstar/chromium.src,ondra-novak/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,littlstar/chromium.src,bright-sparks/chromium-spacewalk,littlstar/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,bright-sparks/chromium-spacewalk,bright-sparks/chromium-spacewalk,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,bright-sparks/chromium-spacewalk,littlstar/chromium.src,bright-sparks/chromium-spacewalk,littlstar/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,bright-sparks/chromium-spacewalk,bright-sparks/chromium-spacewalk,ondra-novak/chromium.src,ondra-novak/chromium.src