[Video] Fix DCHECK crash in PauseVideoIfHidden

[Video] Fix DCHECK crash in PauseVideoIfHidden

WMPI::OnFrameHidden() can get called when the frame is closed.
WMPI::IsHidden() will return false in this case, however it's assumed to
return true in OnFrameHidden and the methods called from there.

BUG=684256
TEST=manual

Review-Url: https://codereview.chromium.org/2653553005
Cr-Commit-Position: refs/heads/master@{#445869}
(cherry picked from commit 5f91d1754a7ffa39cff9619db090b91b8d1b4a98)

Review-Url: https://codereview.chromium.org/2666543003 .
Cr-Commit-Position: refs/branch-heads/2987@{#168}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed: https://chromium.googlesource.com/chromium/src/+/276c7a24aa74d92c9b0139e11850dd128f121528

[whywhat, 2017-01-30 17:54:26]

Description was changed from

==========
[Video] Fix DCHECK crash in PauseVideoIfHidden

WMPI::OnFrameHidden() can get called when the frame is closed.
WMPI::IsHidden() will return false in this case, however it's assumed to
return true in OnFrameHidden and the methods called from there.

BUG=684256
TEST=manual

Review-Url: https://codereview.chromium.org/2653553005
Cr-Commit-Position: refs/heads/master@{#445869}
(cherry picked from commit 5f91d1754a7ffa39cff9619db090b91b8d1b4a98)
==========

to

==========
[Video] Fix DCHECK crash in PauseVideoIfHidden

WMPI::OnFrameHidden() can get called when the frame is closed.
WMPI::IsHidden() will return false in this case, however it's assumed to
return true in OnFrameHidden and the methods called from there.

BUG=684256
TEST=manual

Review-Url: https://codereview.chromium.org/2653553005
Cr-Commit-Position: refs/heads/master@{#445869}
(cherry picked from commit 5f91d1754a7ffa39cff9619db090b91b8d1b4a98)

Review-Url: https://codereview.chromium.org/2666543003 .
Cr-Commit-Position: refs/branch-heads/2987@{#168}
Cr-Branched-From:
ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed:
https://chromium.googlesource.com/chromium/src/+/276c7a24aa74d92c9b0139e11850...
==========

[whywhat, 2017-01-30 17:54:27]

Committed patchset #1 (id:1) manually as
276c7a24aa74d92c9b0139e11850dd128f121528.