Add "arch" and "nacl_arch" query parameter for arm64

BUG=314720
R=qsr@chromium.org,asargent@chromium.org,cpu@chromium.org

Review URL: https://codereview.chromium.org/166033003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252389 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252389