Add an opaqueness hint to GrDrawState.

src/gpu/GrBitmapTextContext.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrBitmapTextContext.h"
 #include "GrAtlas.h"
 #include "GrDrawTarget.h"
@@ skipping 574 matching lines @@
 
     // The texture coords are last in both the with and without color vertex layouts.
     SkPoint* textureCoords = reinterpret_cast<SkPoint*>(
             reinterpret_cast<intptr_t>(positions) + vertSize  - sizeof(SkPoint));
     textureCoords->setRectFan(SkFixedToFloat(texture->normalizeFixedX(tx)),
                               SkFixedToFloat(texture->normalizeFixedY(ty)),
                               SkFixedToFloat(texture->normalizeFixedX(tx + width)),
                               SkFixedToFloat(texture->normalizeFixedY(ty + height)),
                               vertSize);
     if (useColorVerts) {
+        if (0xFF == GrColorUnpackA(fPaint.getColor())) {
+            fDrawTarget->drawState()->setHint(GrDrawState::kVertexColorsAreOpaque_Hint, true);
+        }
         // color comes after position.
         GrColor* colors = reinterpret_cast<GrColor*>(positions + 1);
         for (int i = 0; i < 4; ++i) {
            *colors = fPaint.getColor();
            colors = reinterpret_cast<GrColor*>(reinterpret_cast<intptr_t>(colors) + vertSize);
         }
     }
     fCurrVertex += 4;
 }