Treat deadkey like non-AuraWin Chrome

On Windows, major browsers (Firefox, Internet Explorer, and
non-Aura Chrome) haven't treated deadkey as IME composition.
This CL enables Aura-Win Chrome to behave like non-Aura Chrome.

This CL should also fix Issue 265461 because deadkey
state is now managed only by browser process. We no longer
need the previous hack added as r217633.


BUG=265461
TEST=manually done with US-international keyboard on Win 8.1

Review URL: https://codereview.chromium.org/29843006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230342 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230342