Add support for loading pak files from arbitrary file regions.

base/files/file.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.
 
 #ifndef BASE_FILES_FILE_H_
 #define BASE_FILES_FILE_H_
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
 #include <windows.h>
@@ skipping 137 matching lines @@
     // The last modified time of a file.
     base::Time last_modified;
 
     // The last accessed time of a file.
     base::Time last_accessed;
 
     // The creation time of a file.
     base::Time creation_time;
   };
 
+  // Used to hold information about a region [offset + size] of a file.
+  struct BASE_EXPORT Region {
+    static const Region kWholeFile;
+
+    Region(int64 offset, int64 size);
+
+    bool operator==(const Region& other) const;
+
+    // Start of the region (measured in bytes from the beginning of the file).
+    int64 offset;

[Primiano Tucci (use gerrit), 2014/07/23 23:17:38]

I'm a bit on the fence of this, w.r.t. keeping these fields public, or
converting them to private fields + inline accessors.
The latter would be a bit more bomb-proof and give more sense to the DCHEKS in
the public ctor.
The downside is more code clutter. On the other side we rely on clients of API
to not do stupid things like Region x(0, 10); x.size = 0 //screw you

WDYT?

[willchan no longer on Chromium, 2014/07/25 21:21:23]

I think Region should be a dumb struct. Whatever function accepts Region should
validate the input.

+
+    // Length of the region in bytes.
+    int64 size;
+
+  private:
+    // This ctor is used only by kWholeFile, to construct a zero-sized Region
+    // (which is forbidden by the public ctor) and uniquely identify kWholeFile.
+    Region();
+  };
+
   File();
 
   // Creates or opens the given file. This will fail with 'access denied' if the
   // |name| contains path traversal ('..') components.
   File(const FilePath& name, uint32 flags);
 
   // Takes ownership of |platform_file|.
   explicit File(PlatformFile platform_file);
 
   // Creates an object with a specific error_details code.
@@ skipping 136 matching lines @@
 #endif
 
   Error error_details_;
   bool created_;
   bool async_;
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_H_