Add blend constant color and use it for lcd text common case (no fancy blend or shaded text)

Review URL: http://codereview.appspot.com/4274057/

git-svn-id: http://skia.googlecode.com/svn/trunk@941 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gpu/src/GrGpuGL.h b/gpu/src/GrGpuGL.h
index a731226..ea0c081 100644
--- a/gpu/src/GrGpuGL.h
+++ b/gpu/src/GrGpuGL.h
@@ -132,6 +132,8 @@
     static bool TextureMatrixIsIdentity(const GrGLTexture* texture,
                                         const GrSamplerState& sampler);
 
+    static bool BlendCoefReferencesConstant(GrBlendCoeff coeff);
+
 private:
     // notify callbacks to update state tracking when related
     // objects are bound to GL or deleted outside of the class