Add rewind capability to SkChunkAlloc

include/core/SkChunkAlloc.h

Index: include/core/SkChunkAlloc.h
diff --git a/include/core/SkChunkAlloc.h b/include/core/SkChunkAlloc.h
index e13e2b99c640368ebfbdc5f3e16f6e47f3620807..9699842e6b42a7fab28c9ef8f27fb92fe54fc4d7 100644
--- a/include/core/SkChunkAlloc.h
+++ b/include/core/SkChunkAlloc.h
@@ -22,6 +22,11 @@ public:
      *  pointers.
      */
     void reset();
+    /**
+     *  Reset to 0 used bytes preserving as much memory as possible.
+     *  This invalidates all returned pointers.
+     */
+    void rewind();
 
     enum AllocFailType {
         kReturnNil_AllocFailType,
@@ -43,7 +48,8 @@ public:
 
     size_t totalCapacity() const { return fTotalCapacity; }
     size_t totalUsed() const { return fTotalUsed; }
-    int blockCount() const { return fBlockCount; }
+    SkDEBUGCODE(int blockCount() const { return fBlockCount; })
+    SkDEBUGCODE(size_t totalLost() const { return fTotalLost; })
 
     /**
      *  Returns true if the specified address is within one of the chunks, and
@@ -60,9 +66,13 @@ private:
     size_t  fChunkSize;
     size_t  fTotalCapacity;
     size_t  fTotalUsed;     // will be <= fTotalCapacity
-    int     fBlockCount;
+    SkDEBUGCODE(int     fBlockCount;)
+    SkDEBUGCODE(size_t  fTotalLost;)     // will be <= fTotalCapacity
 
     Block* newBlock(size_t bytes, AllocFailType ftype);
+    Block* addBlockIfNecessary(size_t bytes, AllocFailType ftype);
+
+    SkDEBUGCODE(void validate();)
 };
 
 #endif