[merge to M53] Make sure Widget::dispose() respects UpdateSuspendScope.

BUG=621362

Review-Url: https://codereview.chromium.org/2171683002
Cr-Commit-Position: refs/heads/master@{#406802}
(cherry picked from commit cade7295256e7adabf84272fe5e269834eb44dde)

TBR=dcheng
NOTRY=true
NOPRESUBMIT=true
NOTREECHECKS=true

Review-Url: https://codereview.chromium.org/2190693002
Cr-Commit-Position: refs/branch-heads/2785@{#371}
Cr-Branched-From: 68623971be0cfc492a2cb0427d7f478e7b214c24-refs/heads/master@{#403382}
3 files changed