Add template aliases to support both reference counting and garbage collection for a transition period.

Template aliases are used in clang on which they are currently
supported. The aliases are simple enough that they can be
simulated with simple macros on gcc and msvc.

BUG=

Review URL: https://codereview.chromium.org/137483003

git-svn-id: svn://svn.chromium.org/blink/trunk@165803 bbb929c8-8fbe-4397-9dbb-9b2b20218538