Revert of remove unused SkCachingPixelRef

src/lazy/SkCachingPixelRef.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.
+ */
+
+#ifndef SkCachingPixelRef_DEFINED
+#define SkCachingPixelRef_DEFINED
+
+#include "SkBitmapCache.h"
+#include "SkImageInfo.h"
+#include "SkImageGenerator.h"
+#include "SkPixelRef.h"
+
+class SkColorTable;
+
+/**
+ *  PixelRef which defers decoding until SkBitmap::lockPixels() is
+ *  called.  Caches the decoded images in the global
+ *  SkScaledImageCache.  When the pixels are unlocked, this cache may
+ *  or be destroyed before the next lock.  If so, onLockPixels will
+ *  attempt to re-decode.
+ *
+ *  Decoding is handled by the SkImageGenerator
+ */
+class SkCachingPixelRef : public SkPixelRef {
+public:
+    
+    /**
+     *  Takes ownership of SkImageGenerator.  If this method fails for
+     *  whatever reason, it will return false and immediatetely delete
+     *  the generator.  If it succeeds, it will modify destination
+     *  bitmap.
+     *
+     *  If Install fails or when the SkCachingPixelRef that is
+     *  installed into destination is destroyed, it will call
+     *  `delete` on the generator.  Therefore, generator should be
+     *  allocated with `new`.
+     */
+    static bool Install(SkImageGenerator* gen, SkBitmap* dst);
+
+protected:
+    virtual ~SkCachingPixelRef();
+    bool onNewLockPixels(LockRec*) override;
+    void onUnlockPixels() override;
+    bool onLockPixelsAreWritable() const override { return false; }
+
+    SkData* onRefEncodedData() override {
+        return fImageGenerator->refEncodedData();
+    }
+
+    bool onIsLazyGenerated() const override { return true; }
+
+private:
+    SkImageGenerator* const fImageGenerator;
+    bool                    fErrorInDecoding;
+    const size_t            fRowBytes;
+
+    SkBitmap                fLockedBitmap;
+
+    SkCachingPixelRef(const SkImageInfo&, SkImageGenerator*, size_t rowBytes);
+
+    typedef SkPixelRef INHERITED;
+};
+
+#endif  // SkCachingPixelRef_DEFINED