ObserverList::HasObserver now takes a const pointer.

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 345d7211872ca4eefbe72fff6caf5d14a3fc5260..00f078a6bb2eda580da142bd315cb71ee56ff58d 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -335,7 +335,7 @@ void Compositor::RemoveObserver(CompositorObserver* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
-bool Compositor::HasObserver(CompositorObserver* observer) {
+bool Compositor::HasObserver(const CompositorObserver* observer) const {
   return observer_list_.HasObserver(observer);
 }
 
@@ -349,7 +349,8 @@ void Compositor::RemoveAnimationObserver(
   animation_observer_list_.RemoveObserver(observer);
 }
 
-bool Compositor::HasAnimationObserver(CompositorAnimationObserver* observer) {
+bool Compositor::HasAnimationObserver(
+    const CompositorAnimationObserver* observer) const {
   return animation_observer_list_.HasObserver(observer);
 }