Add an opaqueness hint to GrDrawState.

src/gpu/GrDistanceFieldTextContext.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 "GrDistanceFieldTextContext.h"
 #include "GrAtlas.h"
 #include "SkColorFilter.h"
@@ skipping 403 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 + tw)),
                               SkFixedToFloat(texture->normalizeFixedY(ty + th)),
                               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;
 }
@@ skipping 207 matching lines @@
                                       SkScalarToFixed(x) - (glyph.fAdvanceX >> alignShift),
                                       SkScalarToFixed(y) - (glyph.fAdvanceY >> alignShift),
                                       fontScaler);
             }
             pos += scalarsPerPosition;
         }
     }
 
     this->finish();
 }