Pass file Regions along with FDs to child processes on Android

base/files/memory_mapped_file.h

Index: base/files/memory_mapped_file.h
diff --git a/base/files/memory_mapped_file.h b/base/files/memory_mapped_file.h
index 8a7f045f351a0365d496f37f5824607cacfdc12e..36f2118957df938994100843e265e01fc5afe382 100644
--- a/base/files/memory_mapped_file.h
+++ b/base/files/memory_mapped_file.h
@@ -28,6 +28,7 @@ class BASE_EXPORT MemoryMappedFile {
   struct BASE_EXPORT Region {
     static const Region kWholeFile;
 
+    Region();
     Region(int64 offset, int64 size);
 
     bool operator==(const Region& other) const;
@@ -39,8 +40,7 @@ class BASE_EXPORT MemoryMappedFile {
     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.
+    // Used by kWholeFile.
     Region(base::LinkerInitialized);
   };