|handling_key_event_| flag should be set correctly.
|handling_key_event_| flag should be set correctly.

Fixed the issue that the |handling_key_event_| flag is wrongly set so
that SetComposition (from virtual keyboard) without a physical key event
doesn't work.

TBR=nona@chromium.org
BUG=498633
TEST=Verified on sandbox.

Review URL: https://codereview.chromium.org/1176313002

Cr-Commit-Position: refs/heads/master@{#333906}
(cherry picked from commit 549b1b4ba59b441caef03c8ae318170f218460e0)

Review URL: https://codereview.chromium.org/1180943006.

Cr-Commit-Position: d34a0005849006230ae7ffb1a9693419810a06bc@{#290}
Cr-Branched-From: 40cda19e609fd36fbf5fe489055423e611631abc@{#330231}

Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk