Only drag or maximize / restore when event has not yet been handled.

BUG=332295
TEST=ToplevelWindowEventHandlerTest.DontDragIfModalChild, WorkspaceEventHandlerTest.DoubleClickOrTapWithModalChildDoesntMaximize
TEST=Press Ctrl+O and then try to double click or drag the browser window. It should not move or maximize.

Review URL: https://codereview.chromium.org/144193002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248022 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248022