Break up SkLazyPixelRef functionally into class hierarchy.

src/core/SkScaledImageCache.h

Index: src/core/SkScaledImageCache.h
diff --git a/src/core/SkScaledImageCache.h b/src/core/SkScaledImageCache.h
index fee69d2d58598eb8fee6a7562a45bd2940912e6f..d07a584b915a7ba91ca926237094f45c3410bb69 100644
--- a/src/core/SkScaledImageCache.h
+++ b/src/core/SkScaledImageCache.h
@@ -31,6 +31,8 @@ public:
      *  instance of this cache.
      */
 
+    static SkScaledImageCache* GetGlobalInstance();
+
     static ID* FindAndLock(uint32_t pixelGenerationID,
                            int32_t width,
                            int32_t height,
@@ -59,7 +61,7 @@ public:
 
     ///////////////////////////////////////////////////////////////////////////
 
-    SkScaledImageCache(size_t byteLimit);
+    SkScaledImageCache(size_t byteLimit, SkBaseMutex* mutex = NULL);
     ~SkScaledImageCache();
 
     /**
@@ -114,8 +116,8 @@ public:
      */
     void unlock(ID*);
 
-    size_t getBytesUsed() const { return fBytesUsed; }
-    size_t getByteLimit() const { return fByteLimit; }
+    size_t getBytesUsed() const;
+    size_t getByteLimit() const;
 
     /**
      *  Set the maximum number of bytes available to this cache. If the current
@@ -127,6 +129,8 @@ public:
 public:
     struct Rec;
 private:
+    SkBaseMutex* fMutex;  // can be NULL
+
     Rec*    fHead;
     Rec*    fTail;
 
@@ -154,3 +158,4 @@ private:
 #endif
 };
 #endif
+