Break up SkLazyPixelRef functionally into class hierarchy.

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 "SkImage.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 pure-virtual functions onDecodeInfo()
+ *  and onDecodePixels().  Subclasses of this class need only provide
+ *  those two functions.
+ */
+class SkCachingPixelRef : public SkPixelRef {
+public:
+    SkCachingPixelRef();
+    virtual ~SkCachingPixelRef();
+
+protected:
+    virtual void* onLockPixels(SkColorTable** colorTable) SK_OVERRIDE;
+    virtual void onUnlockPixels() SK_OVERRIDE;
+    virtual bool onLockPixelsAreWritable() const SK_OVERRIDE { return false; }
+    virtual bool onImplementsDecodeInto() SK_OVERRIDE  { return true; }
+    virtual bool onDecodeInto(int pow2, SkBitmap*) SK_OVERRIDE;
+
+    /**
+     *  Configure the supplied bitmap for this pixelRef, based on
+     *  information provided by onDecodeInfo().  Does not set the
+     *  bitmap's pixelRef. */
+    bool configure(SkBitmap* bitmap);
+
+    /**
+     *  Cache info from onDecodeInfo(). Returns false on failure.
+     */
+    bool getInfo(SkImageInfo* info);
+
+    /**
+     *  Return some information about the pixels, allowing this class
+     *  to allocate pixels.  @return false if anything goes wrong.
+     */
+    virtual bool onDecodeInfo(SkImageInfo* info) = 0;
+    /**
+     *  Decode into the given pixels, a block of memory of size
+     *  (info.fHeight - 1) * rowBytes + (info.fWidth * bytesPerPixel)
+     *
+     *  @param info Should be identical to the info returned by
+     *         onDecodeInfo so that the implementation can confirm
+     *         that the caller knows what it is asking for (config,
+     *         size).  Thiscontract also allows the caller to specify
+     *         different output-configs, which the implementation can
+     *         decide to support or not.
+     *
+     *  @return false if anything goes wrong.
+     */
+    virtual bool onDecodePixels(const SkImageInfo& info,
+                                void* pixels,
+                                size_t rowBytes) = 0;
+
+private:
+    bool                        fErrorInDecoding;
+    void*                       fScaledCacheId;
+    SkImageInfo                 fInfo;
+
+    typedef SkPixelRef INHERITED;
+};
+
+#endif  // SkCachingPixelRef_DEFINED
+