Add copyright headers DM.

Review URL: https://codereview.chromium.org/1037713003
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 44090ca..98f0d94 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -1,3 +1,10 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
 #include "CrashHandler.h"
 #include "DMJsonWriter.h"
 #include "DMSrcSink.h"