Remove usage of FOR_EACH_OBSERVER macro in blimp

blimp/engine/app/ui/blimp_screen.cc

Index: blimp/engine/app/ui/blimp_screen.cc
diff --git a/blimp/engine/app/ui/blimp_screen.cc b/blimp/engine/app/ui/blimp_screen.cc
index c10396af01298a574225b75bc9a1aa82ee9f769d..e5d33adbdaad906206261d24c031441e1596c6b5 100644
--- a/blimp/engine/app/ui/blimp_screen.cc
+++ b/blimp/engine/app/ui/blimp_screen.cc
@@ -39,8 +39,8 @@ void BlimpScreen::UpdateDisplayScaleAndSize(float scale,
 
   display_.SetScaleAndBounds(scale, gfx::Rect(size));
 
-  FOR_EACH_OBSERVER(display::DisplayObserver, observers_,
-                    OnDisplayMetricsChanged(display_, metrics));
+  for (auto& observer : observers_)
+    observer.OnDisplayMetricsChanged(display_, metrics);
 }
 
 gfx::Point BlimpScreen::GetCursorScreenPoint() {