Add ChildMessageFilter, a base class for renderer/worker cross-thread MessageFilter

content/worker/worker_thread.cc

Index: content/worker/worker_thread.cc
diff --git a/content/worker/worker_thread.cc b/content/worker/worker_thread.cc
index 53b483aa75a3dd797ee6f43c3d640d2603183bca..74a02747866d2560592c977c92fdf936ff522a5b 100644
--- a/content/worker/worker_thread.cc
+++ b/content/worker/worker_thread.cc
@@ -51,7 +51,7 @@ WorkerThread::WorkerThread() {
 
   indexed_db_message_filter_ = new IndexedDBMessageFilter(
       thread_safe_sender());
-  channel()->AddFilter(indexed_db_message_filter_.get());
+  channel()->AddFilter(indexed_db_message_filter_->GetFilter());
 
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
   SetRuntimeFeaturesDefaultsAndUpdateFromArgs(command_line);
@@ -71,7 +71,7 @@ void WorkerThread::Shutdown() {
   ChildThread::Shutdown();
 
   // Shutdown in reverse of the initialization order.
-  channel()->RemoveFilter(indexed_db_message_filter_.get());
+  channel()->RemoveFilter(indexed_db_message_filter_->GetFilter());
   indexed_db_message_filter_ = NULL;
 
   channel()->RemoveFilter(db_message_filter_.get());