Allow disable WebRTC encryption in Chrome beta channel on Android.

BUG=336743

Review URL: https://codereview.chromium.org/151303003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249718 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249718
Revert "Revert 249127 "Exclude sync strings from Android builds.""

This reverts commit b2af5e1360bb854e9d592212c4d52a7e5950dd43.

Relanding https://codereview.chromium.org/153983006 without removing
the placeholders.

BUG=326023
NOTRY=true

Review URL: https://codereview.chromium.org/156163005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249719 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249719