Revert 159547 "Move keyboard related files from core/ to platform."

> Move keyboard related files from core/ to platform.
> 
> BUG=297477
> TEST=None, trivial move.
> R=abarth@chromium.org
> 
> Review URL: https://codereview.chromium.org/26592011

Gardening. Looks android_clang_dbg failed to compile after r159547.
See
- http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/builds/83650
- http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/builds/83651
- http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/builds/83653

TBR=tfarina@chromium.org

Review URL: https://codereview.chromium.org/27164002

git-svn-id: svn://svn.chromium.org/blink/trunk@159568 bbb929c8-8fbe-4397-9dbb-9b2b20218538