Upstreaming DropShadowImageFilter into skia, from Blink

include/effects/SkDropShadowImageFilter.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkColor.h"
+#include "SkImageFilter.h"
+#include "SkScalar.h"
+
+class SkDropShadowImageFilter : public SkImageFilter {
+public:
+    SkDropShadowImageFilter(SkScalar dx, SkScalar dy, SkScalar sigma, SkColor, SkImageFilter* input = 0);

[Stephen White, 2013/08/06 19:33:37]

Nit: Use NULL instead of 0.

+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDropShadowImageFilter)
+
+protected:
+    explicit SkDropShadowImageFilter(SkFlattenableReadBuffer&);
+    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
+    virtual bool onFilterImage(Proxy*, const SkBitmap& source, const SkMatrix&, SkBitmap* result, SkIPoint* loc) SK_OVERRIDE;
+
+private:
+    SkScalar fDx, fDy, fSigma;
+    SkColor fColor;
+    typedef SkImageFilter INHERITED;
+};