Disk cache: Reference CL for the implementation of file format version 3.

net/disk_cache/file.h

Index: net/disk_cache/file.h
===================================================================
--- net/disk_cache/file.h	(revision 199883)
+++ net/disk_cache/file.h	(working copy)
@@ -67,6 +67,8 @@
   bool SetLength(size_t length);
   size_t GetLength();
 
+  void set_force_creation() { force_creation_ = true; }
+
   // Blocks until |num_pending_io| IO operations complete.
   static void WaitForPendingIO(int* num_pending_io);
 
@@ -84,6 +86,7 @@
  private:
   bool init_;
   bool mixed_;
+  bool force_creation_;
   base::PlatformFile platform_file_;  // Regular, asynchronous IO handle.
   base::PlatformFile sync_platform_file_;  // Synchronous IO handle.