Remove usage of FOR_EACH_OBSERVER macro in ash/

ash/aura/wm_shell_aura.cc

Index: ash/aura/wm_shell_aura.cc
diff --git a/ash/aura/wm_shell_aura.cc b/ash/aura/wm_shell_aura.cc
index 9e0150bc6d91511690b566268a56d1b2aa24bb5e..b316f8df03458eb5a584f73ca76c624374caa2d5 100644
--- a/ash/aura/wm_shell_aura.cc
+++ b/ash/aura/wm_shell_aura.cc
@@ -239,12 +239,13 @@ std::unique_ptr<KeyEventWatcher> WmShellAura::CreateKeyEventWatcher() {
 }
 
 void WmShellAura::OnOverviewModeStarting() {
-  FOR_EACH_OBSERVER(ShellObserver, *shell_observers(),
-                    OnOverviewModeStarting());
+  for (auto& observer : *shell_observers())
+    observer.OnOverviewModeStarting();
 }
 
 void WmShellAura::OnOverviewModeEnded() {
-  FOR_EACH_OBSERVER(ShellObserver, *shell_observers(), OnOverviewModeEnded());
+  for (auto& observer : *shell_observers())
+    observer.OnOverviewModeEnded();
 }
 
 SessionStateDelegate* WmShellAura::GetSessionStateDelegate() {