Create an SkAndroidCodec API separate from SkCodec

src/codec/SkSampledCodec.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 SkSampledCodec_DEFINED
+#define SkSampledCodec_DEFINED
+
+#include "SkAndroidCodec.h"
+#include "SkCodec.h"
+
+/**
+ *  This class implements the functionality of SkAndroidCodec.  Scaling will
+ *  be provided by sampling if it cannot be provided by fCodec.
+ */
+class SkSampledCodec : public SkAndroidCodec {
+public:
+
+    explicit SkSampledCodec(SkCodec*);
+
+    virtual ~SkSampledCodec() {}
+
+protected:
+
+    SkEncodedFormat onGetEncodedFormat() const override { return fCodec->getEncodedFormat(); };
+
+    SkISize onGetSampledDimensions(int sampleSize) const override;
+
+    bool onGetSupportedSubset(SkIRect* desiredSubset) const override { return true; }
+
+    SkCodec::Result onGetAndroidPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
+            AndroidOptions& options) override;
+
+private:
+
+    /**
+     *  This fulfills the same contract as onGetAndroidPixels().
+     *
+     *  We call this function from onGetAndroidPixels() if we have determined
+     *  that fCodec does not support the requested scale, and we need to
+     *  provide the scale by sampling.
+     */
+    SkCodec::Result sampledDecode(const SkImageInfo& info, void* pixels, size_t rowBytes,
+            AndroidOptions& options);
+
+    SkAutoTDelete<SkCodec> fCodec;
+
+    typedef SkAndroidCodec INHERITED;
+};
+#endif // SkSampledCodec_DEFINED