Remove usage of FOR_EACH_OBSERVER macro in gpu

gpu/ipc/service/gpu_command_buffer_stub.cc

Index: gpu/ipc/service/gpu_command_buffer_stub.cc
diff --git a/gpu/ipc/service/gpu_command_buffer_stub.cc b/gpu/ipc/service/gpu_command_buffer_stub.cc
index 6c3063aa446701217dd7816440b705912ac572be..74b419744071f3172560048b503086c3ec6600b4 100644
--- a/gpu/ipc/service/gpu_command_buffer_stub.cc
+++ b/gpu/ipc/service/gpu_command_buffer_stub.cc
@@ -428,9 +428,8 @@ void GpuCommandBufferStub::Destroy() {
     // don't leak resources.
     have_context = decoder_->GetGLContext()->MakeCurrent(surface_.get());
   }
-  FOR_EACH_OBSERVER(DestructionObserver,
-                    destruction_observers_,
-                    OnWillDestroyStub());
+  for (auto& observer : destruction_observers_)
+    observer.OnWillDestroyStub();
 
   if (decoder_) {
     decoder_->Destroy(have_context);