Revert "Move KeyboardCodes and friends to platform/"

This reverts commit http://src.chromium.org/viewvc/blink?revision=160940&view=revision

Per dglazkov, breaks android clang dbg: http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/builds/88545

TBR=dglazkov

Review URL: https://codereview.chromium.org/53963002

git-svn-id: svn://svn.chromium.org/blink/trunk@161007 bbb929c8-8fbe-4397-9dbb-9b2b20218538