bookmarks: Eliminate an unnecessary AsMutable() call.

GetChild() can return a non-const pointer and in this specific situation
inside RemoveAll(), that is more appropriate, and thus we can remove an
unnecessary AsMutable() call.

BUG=330331
R=brettw@chromium.org

Review URL: https://codereview.chromium.org/102073010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242510 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242510
This CL refactors ToplevelWindowEventHandler and TwoFingerDragHandler to make merging the two easier.

Notable changes:
- Fixed weirdness due to initiating tab dragging while a different drag is in progress.
- Makes it no longer possible to alter the window's show type via a fling while resizing (vs moving) the window.
- Moved all of the code to set the state when beginning / completing a drag to ToplevelWindowEventHandler::AttemptToStartDrag() and
ToplevelWindowEventHandler::CompleteDrag()
- Removed unneeded code to animate to the side snapped states
- Made the instances where ToplevelWindowEventHandler::OnGestureEvent() stops propagation more obvious

BUG=324038
TEST=ToplevelWindowEventHandlerTest.RunMoveLoopRevertsInProgressDrag

Review URL: https://codereview.chromium.org/115863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242511 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242511