Add support for loading pak files from arbitrary file regions.

base/files/file.h

Index: base/files/file.h
diff --git a/base/files/file.h b/base/files/file.h
index 1913bc7f6c408c8e1e3840da712895ff2fd88259..9bd70ed2d845cb001cbeb8d74639a2354f7dfc96 100644
--- a/base/files/file.h
+++ b/base/files/file.h
@@ -155,6 +155,26 @@ class BASE_EXPORT 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