Remove all remaining traces of MessageLoopProxy.

blimp/engine/session/blimp_engine_session.cc

Index: blimp/engine/session/blimp_engine_session.cc
diff --git a/blimp/engine/session/blimp_engine_session.cc b/blimp/engine/session/blimp_engine_session.cc
index bbd18e56fe60ffc4507d0e0d9e9dd35ea4c3ffc4..70134b671f01cbcba85f928a93333bf16cd2911b 100644
--- a/blimp/engine/session/blimp_engine_session.cc
+++ b/blimp/engine/session/blimp_engine_session.cc
@@ -302,10 +302,10 @@ void BlimpEngineSession::GetEnginePortForTesting(
 }
 
 void BlimpEngineSession::RegisterFeatures() {
-  thread_pipe_manager_.reset(new ThreadPipeManager(
-      content::BrowserThread::GetMessageLoopProxyForThread(
-          content::BrowserThread::IO),
-      net_components_->GetBrowserConnectionHandler()));
+  thread_pipe_manager_.reset(
+      new ThreadPipeManager(content::BrowserThread::GetTaskRunnerForThread(
+                                content::BrowserThread::IO),
+                            net_components_->GetBrowserConnectionHandler()));
 
   // Register features' message senders and receivers.
   tab_control_message_sender_ =