Allow GrGLEffects to produce variable length keys.

R=robertphillips@google.com, jvanverth@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/385713005
diff --git a/src/gpu/effects/GrTextureDomain.h b/src/gpu/effects/GrTextureDomain.h
index dc78187..80a617e 100644
--- a/src/gpu/effects/GrTextureDomain.h
+++ b/src/gpu/effects/GrTextureDomain.h
@@ -108,7 +108,7 @@
          * GrGLEffect::GenKey() must call this and include the returned value in it's computed key.
          * The returned will be limited to the lower kDomainKeyBits bits.
          */
-        static GrGLEffect::EffectKey DomainKey(const GrTextureDomain& domain) {
+        static uint32_t DomainKey(const GrTextureDomain& domain) {
             GR_STATIC_ASSERT(kModeCount <= 4);
             return domain.mode();
         }