Add support for loading pak files from arbitrary file regions.

ui/base/resource/data_pack.h

 // Copyright (c) 2012 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.
 
 // DataPack represents a read-only view onto an on-disk file that contains
 // (key, value) pairs of data.  It's used to store static resources like
 // translation strings and images.
 
 #ifndef UI_BASE_RESOURCE_DATA_PACK_H_
 #define UI_BASE_RESOURCE_DATA_PACK_H_
@@ skipping 20 matching lines @@
  public:
   DataPack(ui::ScaleFactor scale_factor);
   virtual ~DataPack();
 
   // Load a pack file from |path|, returning false on error.
   bool LoadFromPath(const base::FilePath& path);
 
   // Loads a pack file from |file|, returning false on error.
   bool LoadFromFile(base::File file);
 
+  // Loads a pack file from |region| of |file|, returning false on error.
+  bool LoadFromFileRegion(base::File file, const base::File::Region& region);
+
   // Writes a pack file containing |resources| to |path|. If there are any
   // text resources to be written, their encoding must already agree to the
   // |textEncodingType| specified. If no text resources are present, please
   // indicate BINARY.
   static bool WritePack(const base::FilePath& path,
                         const std::map<uint16, base::StringPiece>& resources,
                         TextEncodingType textEncodingType);
 
   // ResourceHandle implementation:
   virtual bool HasResource(uint16 resource_id) const OVERRIDE;
@@ skipping 20 matching lines @@
   // The scale of the image in this resource pack relative to images in the 1x
   // resource pak.
   ui::ScaleFactor scale_factor_;
 
   DISALLOW_COPY_AND_ASSIGN(DataPack);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_RESOURCE_DATA_PACK_H_