Reduce FOR_EACH_OBSERVER usage in ui/

ui/ozone/platform/drm/mus_thread_proxy.cc

Index: ui/ozone/platform/drm/mus_thread_proxy.cc
diff --git a/ui/ozone/platform/drm/mus_thread_proxy.cc b/ui/ozone/platform/drm/mus_thread_proxy.cc
index dd1c5d747f770d0588c9151f26da962037bd6601..c70850aea21525270c4bde41976abc6cd6bde1fd 100644
--- a/ui/ozone/platform/drm/mus_thread_proxy.cc
+++ b/ui/ozone/platform/drm/mus_thread_proxy.cc
@@ -42,8 +42,8 @@ void MusThreadProxy::InitializeOnEvdev() {}
 
 MusThreadProxy::~MusThreadProxy() {
   DCHECK(on_window_server_thread_.CalledOnValidThread());
-  FOR_EACH_OBSERVER(GpuThreadObserver, gpu_thread_observers_,
-                    OnGpuThreadRetired());
+  for (GpuThreadObserver& observer : gpu_thread_observers_)
+    observer.OnGpuThreadRetired();
 }
 
 // This is configured on the GPU thread.
@@ -74,8 +74,8 @@ void MusThreadProxy::DispatchObserversFromDrmThread() {
 
 void MusThreadProxy::RunObservers() {
   DCHECK(on_window_server_thread_.CalledOnValidThread());
-  FOR_EACH_OBSERVER(GpuThreadObserver, gpu_thread_observers_,
-                    OnGpuThreadReady());
+  for (GpuThreadObserver& observer : gpu_thread_observers_)
+    observer.OnGpuThreadReady();
 }
 
 void MusThreadProxy::AddGpuThreadObserver(GpuThreadObserver* observer) {