Move Preload() code to MappedFile

net/disk_cache/blockfile/mapped_file.h

Index: net/disk_cache/blockfile/mapped_file.h
diff --git a/net/disk_cache/blockfile/mapped_file.h b/net/disk_cache/blockfile/mapped_file.h
index 8a1e40fa6ce961e46e63a7badbb901c64ad3b556..f0efa41ed77fd4dcfaf1b1050d1352068132f770 100644
--- a/net/disk_cache/blockfile/mapped_file.h
+++ b/net/disk_cache/blockfile/mapped_file.h
@@ -46,6 +46,10 @@ class NET_EXPORT_PRIVATE MappedFile : public File {
   // Flush the memory-mapped section to disk (synchronously).
   void Flush();
 
+  // Heats up the file system cache and make sure the file is fully
+  // readable (synchronously).
+  bool Preload();
+
  private:
   virtual ~MappedFile();