Added premulFourChannelColor to GrInvariantOutput

include/gpu/GrInvariantOutput.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrInvariantOutput_DEFINED
 #define GrInvariantOutput_DEFINED
 
@@ skipping 179 matching lines @@
                 fColor = GrColorPackRGBA(a, a, a, a);
                 fValidFlags = kRGBA_GrColorComponentFlags;
             } else {
                 fValidFlags = kNone_GrColorComponentFlags;
             }
             fIsSingleComponent = true;
         }
         SkDEBUGCODE(this->validate());
     }
 
+    void premulFourChannelColor() {
+        SkDEBUGCODE(this->validate());
+        SkASSERT(!fIsSingleComponent);
+        fNonMulStageFound = true;
+        if (!(fValidFlags & kA_GrColorComponentFlag)) {
+            fValidFlags = kNone_GrColorComponentFlags;
+        } else {
+            fColor = GrPremulColor(fColor);
+        }
+        SkDEBUGCODE(this->validate());
+    }
+
     void invalidateComponents(GrColorComponentFlags invalidateFlags, ReadInput readsInput) {
         SkDEBUGCODE(this->validate());
         fValidFlags = (fValidFlags & ~invalidateFlags);
         fIsSingleComponent = false;
         fNonMulStageFound = true;
         if (kWillNot_ReadInput == readsInput) {
             fWillUseInputColor = false;
         }
         SkDEBUGCODE(this->validate());
     }
@@ skipping 111 matching lines @@
     GrColorComponentFlags fValidFlags;
     bool fIsSingleComponent;
     bool fNonMulStageFound;
     bool fWillUseInputColor;
     bool fIsLCDCoverage; // Temorary data member until texture pixel configs are updated
 
 };
 
 #endif