Disk cache: Add a hash to the entry's internal data.

net/disk_cache/storage_block.h

Index: net/disk_cache/storage_block.h
===================================================================
--- net/disk_cache/storage_block.h	(revision 110637)
+++ net/disk_cache/storage_block.h	(working copy)
@@ -61,6 +61,9 @@
   // Returns true if there is data associated with this object.
   bool HasData() const;
 
+  // Returns true if the internal hash is correct.
+  bool VerifyHash() const;
+
   // Returns true if this object owns the data buffer, false if it is shared.
   bool own_data() const;
 
@@ -73,6 +76,7 @@
  private:
   void AllocateData();
   void DeleteData();
+  uint32 CalculateHash() const;
 
   T* data_;
   MappedFile* file_;