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- record the original state when the gesture starts
- changes the height condition for the closest state based on the
  original state
- limit the fling handling only when the closest state ends up with
  the original state. This will save the most of the case, however
  it may cause unexpected results if the user makes complicated
  gestures (like moves up from minimized, up to the full-screen,
  then fling-down). I think this is a rare case and we don't
  have to care about.

BUG=415211
R=pkotwicz@chromium.org
TEST=athena_unittests && manually

Review URL: https://codereview.chromium.org/581933004

Cr-Commit-Position: refs/heads/master@{#295616}