Fix DCHECK crash inside SetMaximizedOrFullscreenBounds.

If the set bounds event was meant to be animated, and occurred during a
drag, then it would trigger the DCHECK in
SetMaximizedOrFullscreenBounds.

Bug: 941017
Test: No DCHECK on finishing dragging a PIP window.
Change-Id: I9ced916fa8f7eafbac2df232b3abe242a704a329
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1523126
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Eliot Courtney <edcourtney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641083}
1 file changed