Use vertex attribute for text color in GrBitmapTextContext to make batching more likely

src/gpu/GrBitmapTextContext.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrBitmapTextContext_DEFINED
 #define GrBitmapTextContext_DEFINED
 
@@ skipping 27 matching lines @@
     void flushGlyphs();                 // automatically called by destructor
     void finish();
 
     enum {
         kMinRequestedGlyphs      = 1,
         kDefaultRequestedGlyphs  = 64,
         kMinRequestedVerts       = kMinRequestedGlyphs * 4,
         kDefaultRequestedVerts   = kDefaultRequestedGlyphs * 4,
     };
 
-    SkPoint*                fVertices;
+    void*                   fVertices;
     int32_t                 fMaxVertices;
     GrTexture*              fCurrTexture;
     int                     fCurrVertex;
     SkRect                  fVertexBounds;
 };
 
 #endif