Add fallback code for TextContexts that don't support all features

include/gpu/GrDistanceFieldTextContext.h

Index: include/gpu/GrDistanceFieldTextContext.h
diff --git a/include/gpu/GrDistanceFieldTextContext.h b/include/gpu/GrDistanceFieldTextContext.h
index 172342a0f0061c21c55d9f86766802d7fc994d2d..8b94038b678429b72d31f35457e8ad6264cd3e7f 100755
--- a/include/gpu/GrDistanceFieldTextContext.h
+++ b/include/gpu/GrDistanceFieldTextContext.h
@@ -21,6 +21,8 @@ public:
     virtual void drawPosText(const char text[], size_t byteLength,
                              const SkScalar pos[], SkScalar constY,
                              int scalarsPerPosition) SK_OVERRIDE;
+    
+    static bool CanDraw(const SkPaint& paint, const SkMatrix& ctm);
 
 private:
     GrDistanceFieldTextContext(GrContext*, const GrPaint&, const SkPaint&,