[Mac] Refactor the logic of tab dragging out of TabView and into a new helper.
The helper TabStripDragController is owned by the TabStripController. It
operates using the TabDraggingEventTarget protocol, which is used to pass the
mouse events from the TabView up through various controllers to the DragController.
This CL introduces no behavioral changes and is just preparatory work for being
able to drag multiple tabs.
BUG=78816
TEST=Drag tabs in and out of the tab strip. Everything works as before.
Review URL: http://codereview.chromium.org/7080064
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@88125 0039d316-1c4b-4281-b951-d872f2087c98
11 files changed
