Simplify resolution of mojo: URLs.

shell/filename_util.h

Index: shell/filename_util.h
diff --git a/shell/filename_util.h b/shell/filename_util.h
index 10fa8fe0b51c5b1991a1a6218fa0b42470522364..4dae84a77cf8cd249afdfbfbf237bfb06730ec91 100644
--- a/shell/filename_util.h
+++ b/shell/filename_util.h
@@ -17,6 +17,10 @@ namespace mojo {
 // may not be valid if the input is malformed.
 GURL FilePathToFileURL(const base::FilePath& path);
 
+// This URL is going to be treated as a directory. Ensure there is a trailing
+// slash so that GURL.Resolve(...) works correctly.
+GURL AddTrailingSlashIfNeeded(const GURL& url);
+
 }  // namespace mojo
 
 #endif  // SHELL_FILENAME_UTIL_H_