Invalidate native custom element support for virtual keyboard

Polymer is currently broken when native CustomElement is
turned on. This CL invalidate CustomElement native support
for VK. We will re-enable it once polymer works well with
native custom element.

BUG=NONE

Review URL: https://codereview.chromium.org/95813002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237854 0039d316-1c4b-4281-b951-d872f2087c98
Add PRESUBMIT disallowing msvs_cygwin_shell

build/common.gypi now has the default set to 0, avoid using 1 or
introducing more uses of manual setting to 0. Only checks the
diff, not the full file, so shouldn't be annoying.

R=maruel@chromium.org
BUG=123026

Review URL: https://codereview.chromium.org/93543002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237855 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237855