Export shader variables from the translator DLL. This will allow us to use these methods when compiling the translator as a DLL. BUG=angle:466,697 Change-Id: Ic9169fb7c69fe0bf5f98addfc128a30ee6b2159d Reviewed-on: https://chromium-review.googlesource.com/208752 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org>