Makes hiding window conditional when escape is pressed in move loop

Hiding makes sense if a new browser window was created for the drag
(as escape=revert, which means we're going to destroy the
window). But if the drag isn't because of a new window (you selected
all the tabs in a window and started dragging), then revert should
move the window backs to its start location and stop.

BUG=297054
TEST=see bug
R=ben@chromium.org

Review URL: https://codereview.chromium.org/24378002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225189 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225189