Move most of extension_file_util.cc into extensions/common/file_util.cc

chrome/browser/extensions/unpacked_installer.h

Index: chrome/browser/extensions/unpacked_installer.h
diff --git a/chrome/browser/extensions/unpacked_installer.h b/chrome/browser/extensions/unpacked_installer.h
index fea1f59cc1f4a525ec8dad5f6a143ed0c9c4ac04..73924a6f6797c27bcef1bb3576d1e4e3f1daf7bc 100644
--- a/chrome/browser/extensions/unpacked_installer.h
+++ b/chrome/browser/extensions/unpacked_installer.h
@@ -85,7 +85,7 @@ class UnpackedInstaller
   // the UI thread. In turn, once that gets the pref, it goes back to the
   // file thread with LoadWithFileAccess.
   // TODO(yoz): It would be nice to remove this ping-pong, but we need to know
-  // what file access flags to pass to extension_file_util::LoadExtension.
+  // what file access flags to pass to file_util::LoadExtension.
   void GetAbsolutePath();
   void CheckExtensionFileAccess();
   void LoadWithFileAccess(int flags);