Revert 289224 "Update ui::CompositorObserver instrumentation"

trunk/src/ui/compositor/compositor.cc

Index: trunk/src/ui/compositor/compositor.cc
===================================================================
--- trunk/src/ui/compositor/compositor.cc	(revision 289228)
+++ trunk/src/ui/compositor/compositor.cc	(working copy)
@@ -233,8 +233,10 @@
 }
 
 void Compositor::AddObserver(CompositorObserver* observer) {
-#if DCHECK_IS_ON
-  DCHECK(observer);
+#if defined(OS_MACOSX)
+  // Debugging instrumentation for crbug.com/401630.
+  // TODO(ccameron): remove this.
+  CHECK(observer);
   if (!observer_list_.HasObserver(observer))
     observer->observing_count_ += 1;
 #endif
@@ -243,7 +245,9 @@
 }
 
 void Compositor::RemoveObserver(CompositorObserver* observer) {
-#if DCHECK_IS_ON
+#if defined(OS_MACOSX)
+  // Debugging instrumentation for crbug.com/401630.
+  // TODO(ccameron): remove this.
   if (observer_list_.HasObserver(observer))
     observer->observing_count_ -= 1;
 #endif