Add function for logging blend info on XP.

src/gpu/gl/GrGLGpu.h

Index: src/gpu/gl/GrGLGpu.h
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index 016547fad3b0e7b16033301b120decd86033db9c..e1bc869497b96a3c54c191f2805036599aacad3f 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -446,9 +446,9 @@ private:
         TriState        fEnabled;
 
         void invalidate() {
-            fEquation = kInvalid_GrBlendEquation;
-            fSrcCoeff = kInvalid_GrBlendCoeff;
-            fDstCoeff = kInvalid_GrBlendCoeff;
+            fEquation = static_cast<GrBlendEquation>(-1);
+            fSrcCoeff = static_cast<GrBlendCoeff>(-1);
+            fDstCoeff = static_cast<GrBlendCoeff>(-1);
             fConstColorValid = false;
             fEnabled = kUnknown_TriState;
         }