expand unitests for color4f

include/core/SkShader.h

Index: include/core/SkShader.h
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index bf6d6ddb42fd59c148a25b4991aa0b911077c368..297091d54206fe64b427f5760c70bb8a07086d81 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -121,6 +121,10 @@ public:
          */
         virtual uint32_t getFlags() const { return 0; }
 
+        bool supports4f() const {
+            return SkToBool(this->getFlags() & kSupports4f_Flag);
+        }
+
         /**
          *  Called for each span of the object being drawn. Your subclass should
          *  set the appropriate colors (with premultiplied alpha) that correspond