Remove usage of base::ObserverList<T>::Iter::GetNext() in //content.

content/public/test/mock_render_thread.cc

Index: content/public/test/mock_render_thread.cc
diff --git a/content/public/test/mock_render_thread.cc b/content/public/test/mock_render_thread.cc
index f28f88f8530fffa7a445e9afa1b435d7c32fb229..e93d645fb768a2b38875aada213cbcb328a7a493 100644
--- a/content/public/test/mock_render_thread.cc
+++ b/content/public/test/mock_render_thread.cc
@@ -269,10 +269,8 @@ void MockRenderThread::OnCreateChildFrame(
 }
 
 bool MockRenderThread::OnControlMessageReceived(const IPC::Message& msg) {
-  base::ObserverListBase<RenderThreadObserver>::Iterator it(&observers_);
-  RenderThreadObserver* observer;
-  while ((observer = it.GetNext()) != NULL) {
-    if (observer->OnControlMessageReceived(msg))
+  for (auto& observer : observers_) {
+    if (observer.OnControlMessageReceived(msg))
       return true;
   }
   return OnMessageReceived(msg);