Use vertex attribute for text color in GrBitmapTextContext

R=jvanverth@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/316063002
diff --git a/src/gpu/GrBitmapTextContext.h b/src/gpu/GrBitmapTextContext.h
index 23248eb..51193c8 100644
--- a/src/gpu/GrBitmapTextContext.h
+++ b/src/gpu/GrBitmapTextContext.h
@@ -45,7 +45,7 @@
         kDefaultRequestedVerts   = kDefaultRequestedGlyphs * 4,
     };
 
-    SkPoint*                fVertices;
+    void*                   fVertices;
     int32_t                 fMaxVertices;
     GrTexture*              fCurrTexture;
     int                     fCurrVertex;