[Android] Expose isSystemLayoutDirectionRtl() to c++.

On Android, locale direction is not necessarily UI layout
direction. For example, Hebrew on 4.1 is still LTR layout
because RTL layout direction support is from 4.2. So in
general, we should rely on layout direction, not locale.

Phone tab switcher was using IsRTL() function which only
depends on locale. So expose isSystemLayoutDirectionRtl()
to c++ world so that we can fix the phone tab switcher
layout direction.

In addition, we cache the layout direction.

NOTRY=true
BUG=320120

Review URL: https://codereview.chromium.org/160733002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252390 0039d316-1c4b-4281-b951-d872f2087c98
Correctly handle "Global accessibility mode" toggle action on chrome://accessibility in Win8.

BUG=343865

Review URL: https://codereview.chromium.org/170963002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252391 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252391