Move LazyResource::resolveImpl to the cpp. This avoids a compile error where GCC is not compatible with MSVS and Clang, who can both handle calls to forward declared functions in templates. It explicitly specializes LazyResource for the used template types. BUG=angleproject:2182 Change-Id: Iedb1f157d0662b0ea4472c9b4e85828217be577e Reviewed-on: https://chromium-review.googlesource.com/757758 Reviewed-by: Jeff Gilbert <jgilbert@mozilla.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>