Add support for loading pak files from arbitrary file regions.

base/files/memory_mapped_file.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_FILES_MEMORY_MAPPED_FILE_H_
 #define BASE_FILES_MEMORY_MAPPED_FILE_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/files/file.h"
@@ skipping 17 matching lines @@
   // read only. If this object already points to a valid memory mapped file
   // then this method will fail and return false. If it cannot open the file,
   // the file does not exist, or the memory mapping fails, it will return false.
   // Later we may want to allow the user to specify access.
   bool Initialize(const FilePath& file_name);
 
   // As above, but works with an already-opened file. MemoryMappedFile takes
   // ownership of |file| and closes it when done.
   bool Initialize(File file);
 
+  // As above, but works with a region of an already-opened file.
+  bool Initialize(File file, const base::File::Region& region);
+
 #if defined(OS_WIN)
   // Opens an existing file and maps it as an image section. Please refer to
   // the Initialize function above for additional information.
   bool InitializeAsImageSection(const FilePath& file_name);
 #endif  // OS_WIN
 
   const uint8* data() const { return data_; }
   size_t length() const { return length_; }
 
   // Is file_ a valid file handle that points to an open, memory mapped file?
   bool IsValid() const;
 
  private:
   // Map the file to memory, set data_ to that memory address. Return true on
   // success, false on any kind of failure. This is a helper for Initialize().
-  bool MapFileToMemory();
+  bool MapFileToMemory(const base::File::Region& region);
 
   // Closes all open handles.
   void CloseHandles();
 
   File file_;
   uint8* data_;
   size_t length_;
 
 #if defined(OS_WIN)
   win::ScopedHandle file_mapping_;
   bool image_;  // Map as an image.
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile);
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_MEMORY_MAPPED_FILE_H_