Add SkCachedData and use it for SkMipMap

src/core/SkResourceCache.h

Index: src/core/SkResourceCache.h
diff --git a/src/core/SkResourceCache.h b/src/core/SkResourceCache.h
index 52196985d392cd327516f3dd97a7853955ba8c9a..665c0be498518008c3531728d0680ab6bcee25c6 100644
--- a/src/core/SkResourceCache.h
+++ b/src/core/SkResourceCache.h
@@ -10,6 +10,7 @@
 
 #include "SkBitmap.h"
 
+class SkCachedData;
 class SkDiscardableMemory;
 class SkMipMap;
 
@@ -197,6 +198,8 @@ public:
     DiscardableFactory discardableFactory() const { return fDiscardableFactory; }
     SkBitmap::Allocator* allocator() const { return fAllocator; };
 
+    SkCachedData* newCachedData(size_t bytes);
+
     /**
      *  Call SkDebugf() with diagnostic information about the state of the cache
      */