Add SkWebpCodec, for decoding .webp images.

src/codec/SkWebpCodec.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkWebpCodec_DEFINED
+#define SkWebpCodec_DEFINED
+
+#include "SkCodec.h"
+#include "SkEncodedFormat.h"
+#include "SkImageInfo.h"
+#include "SkTypes.h"
+
+class SkStream;
+
+class SkWebpCodec final : public SkCodec {
+public:
+    // Assumes IsWebp was called and returned true.
+    static SkCodec* NewFromStream(SkStream*);
+    static bool IsWebp(SkStream*);
+protected:
+    Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*)
+            override;
+    SkEncodedFormat onGetEncodedFormat() const override { return kWEBP_SkEncodedFormat; }
+
+    bool onReallyHasAlpha() const override {
+        return this->getInfo().alphaType() != kOpaque_SkAlphaType;
+    }
+
+    SkISize onGetScaledDimensions(float desiredScale) const override;
+private:
+    SkWebpCodec(const SkImageInfo&, SkStream*);
+
+    typedef SkCodec INHERITED;
+};
+#endif // SkWebpCodec_DEFINED