It looks big, but most of change is simple signature change.

 Note: I need your advice on how to deal with WM_CHAR event on Win. Please see my comment below.

BUG=none
TEST=no new functionality. All tests should still pass.

Review URL: http://codereview.chromium.org/6034002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70553 0039d316-1c4b-4281-b951-d872f2087c98