Remove gpu shader optimatization for solid white or trans black colors

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 533 matching lines @@
          */
         kInvalid_BlendOptFlag        = 0x20,
     };
     GR_DECL_BITFIELD_OPS_FRIENDS(BlendOptFlags);
 
     void invalidateBlendOptFlags() {
         fBlendOptFlags = kInvalid_BlendOptFlag;
     }
 
     /**
+     * We don't use suplied vertex color attributes if our blend mode is EmitCoverage or
+     * EmitTransBlack
+     */
+    bool canIgnoreColorAttribute() const;
+
+    /**
      * Determines what optimizations can be applied based on the blend. The coefficients may have
      * to be tweaked in order for the optimization to work. srcCoeff and dstCoeff are optional
      * params that receive the tweaked coefficients. Normally the function looks at the current
      * state to see if coverage is enabled. By setting forceCoverage the caller can speculatively
      * determine the blend optimizations that would be used if there was partial pixel coverage.
      *
      * Subclasses of GrDrawTarget that actually draw (as opposed to those that just buffer for
      * playback) must call this function and respect the flags that replace the output color.
      *
      * If the cached BlendOptFlags does not have the invalidate bit set, then getBlendOpts will
@@ skipping 439 matching lines @@
      *  @param count      the number of attributes being set, limited to kMaxVertexAttribCnt.
      */
     void setVertexAttribs(const GrVertexAttrib attribs[], int count);
 
     typedef SkRefCnt INHERITED;
 };
 
 GR_MAKE_BITFIELD_OPS(GrDrawState::BlendOptFlags);
 
 #endif