DevTools: fix DevTools Window lifetime with fast_unload_controller

In case of undocked DevTools, we rely on NOTIFICATION_TAB_CLOSING to
figure out the moment to destroy DevTools window. However,
fast_unload_controller detaches WebContents from browser after
receivign beforeunload ack, so we'll never destroy associated
DevTools window.

This patch triggers DevTools window destruction in result of
WebContentsDestroyed callback on front_end WebContents.

BUG=315502
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/61553004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233269 0039d316-1c4b-4281-b951-d872f2087c98
Makes MouseWatcher work while in metro mode

I'm changing the aura implementation to use
Env::AddPreTargetListener. This way I don't need MessageLoop specific
code and it'll work correctly for win on both metro and non-metro.

BUG=315155
TEST=none
R=ben@chromium.org

Review URL: https://codereview.chromium.org/60443003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233270 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233270