Move DBMessageFilter to content/child since its only used in child ptypes

content/child/db_message_filter.h

Index: content/child/db_message_filter.h
diff --git a/content/common/db_message_filter.h b/content/child/db_message_filter.h
similarity index 89%
rename from content/common/db_message_filter.h
rename to content/child/db_message_filter.h
index ac157ff1e0e9f440e6c1d9f765318c9153b1ed77..100d74249d71acb7fff233272b6070399f25790b 100644
--- a/content/common/db_message_filter.h
+++ b/content/child/db_message_filter.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CONTENT_COMMON_DB_MESSAGE_FILTER_H_
-#define CONTENT_COMMON_DB_MESSAGE_FILTER_H_
+#ifndef CONTENT_CHILD_DB_MESSAGE_FILTER_H_
+#define CONTENT_CHILD_DB_MESSAGE_FILTER_H_
 
 #include "ipc/ipc_channel_proxy.h"
 
@@ -34,4 +34,4 @@ class DBMessageFilter : public IPC::ChannelProxy::MessageFilter {
 
 }  // namespace content
 
-#endif  // CONTENT_COMMON_DB_MESSAGE_FILTER_H_
+#endif  // CONTENT_CHILD_DB_MESSAGE_FILTER_H_