Add isUnblended query to GrDrawState.

src/gpu/GrDrawState.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrDrawState_DEFINED
 #define GrDrawState_DEFINED
 
@@ skipping 141 matching lines @@
      * intends to specify fractional pixel coverage (via setCoverage(), through a coverage vertex
      * attribute, or a coverage effect) but may not have specified it yet.
      */
     bool couldApplyCoverage(const GrDrawTargetCaps& caps) const;
 
     /**
      * Determines whether the output coverage is guaranteed to be one for all pixels hit by a draw.
      */
     bool hasSolidCoverage() const;
 
+    /**
+     * This function returns true if the render target destination pixel values will be read for
+     * blending during draw.
+     */
+    bool willBlendWithDst() const;
+
     /// @}
 
     ///////////////////////////////////////////////////////////////////////////
     /// @name Color
     ////
 
     GrColor getColor() const { return fColor; }
 
     /**
      *  Sets color for next draw to a premultiplied-alpha color.
@@ skipping 661 matching lines @@
     int fFixedFunctionVertexAttribIndices[kGrFixedFunctionVertexAttribBindingCnt];
 
     friend class GrOptDrawState;
 
     typedef SkRefCnt INHERITED;
 };
 
 GR_MAKE_BITFIELD_OPS(GrDrawState::BlendOptFlags);
 
 #endif