Add clip effect for circles

src/gpu/effects/GrOvalEffect.h

Index: src/gpu/effects/GrOvalEffect.h
diff --git a/src/gpu/effects/GrOvalEffect.h b/src/gpu/effects/GrOvalEffect.h
new file mode 100644
index 0000000000000000000000000000000000000000..796ee5befb5790bd8fc586e24f8e5631ff8769df
--- /dev/null
+++ b/src/gpu/effects/GrOvalEffect.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrOvalEffect_DEFINED
+#define GrOvalEffect_DEFINED
+
+#include "GrTypes.h"
+#include "GrTypesPriv.h"
+
+class GrEffectRef;
+struct SkRect;
+
+namespace GrOvalEffect {
+    /**
+     * Creates an effect that performs clipping against an oval.
+     */
+    GrEffectRef* Create(GrEffectEdgeType, const SkRect&);
+};
+
+#endif