Fix the problem that releasing a key after pressing multiple modifiers corrupts keyboard overlay
Fix the problem that releasing a key after pressing multiple modifiers corrupts keyboard overlay

BUG=chromium-os:14237
TEST=tested manually

Review URL: http://codereview.chromium.org/6873045
Patch from Ryo Hashimoto <hashimoto@chromium.org>.

git-svn-id: http://src.chromium.org/svn/trunk/src@82062 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 0b57b0f948f3a25e6132590c0eedbed22a29fec2
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser