Attempt at fixing tab dragging crash. I believe the crash is happening because there is an existing TabDragController when a new one is created. Right after we create the new TabDragController it replaces the old, but if we create the new one before the old is destroyed it means the old is still set as a delegate on the TabContents so that when the new restores the delegates it restores the old TabDragController, which has now been deleted.
Attempt at fixing tab dragging crash. I believe the crash is happening
because there is an existing TabDragController when a new one is
created. Right after we create the new TabDragController it replaces
the old, but if we create the new one before the old is destroyed it
means the old is still set as a delegate on the TabContents so that
when the new restores the delegates it restores the old
TabDragController, which has now been deleted.

BUG=107172
TEST=none
R=ben@chromium.org


Review URL: http://codereview.chromium.org/8915026

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@114653 0039d316-1c4b-4281-b951-d872f2087c98

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