Update ui::CompositorObserver instrumentation

ui/compositor/compositor.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/compositor/compositor.h"
 
 #include <algorithm>
 #include <deque>
 
 #include "base/bind.h"
@@ skipping 260 matching lines @@
 void Compositor::SetBackgroundColor(SkColor color) {
   host_->set_background_color(color);
   ScheduleDraw();
 }
 
 scoped_refptr<CompositorVSyncManager> Compositor::vsync_manager() const {
   return vsync_manager_;
 }
 
 void Compositor::AddObserver(CompositorObserver* observer) {
-#if defined(OS_MACOSX)
-  // Debugging instrumentation for crbug.com/401630.
-  // TODO(ccameron): remove this.
-  CHECK(observer);
+#if DCHECK_IS_ON
+  DCHECK(observer);
   if (!observer_list_.HasObserver(observer))
     observer->observing_count_ += 1;
 #endif
 
   observer_list_.AddObserver(observer);
 }
 
 void Compositor::RemoveObserver(CompositorObserver* observer) {
-#if defined(OS_MACOSX)
-  // Debugging instrumentation for crbug.com/401630.
-  // TODO(ccameron): remove this.
+#if DCHECK_IS_ON
   if (observer_list_.HasObserver(observer))
     observer->observing_count_ -= 1;
 #endif
 
   observer_list_.RemoveObserver(observer);
 }
 
 bool Compositor::HasObserver(CompositorObserver* observer) {
   return observer_list_.HasObserver(observer);
 }
@@ skipping 132 matching lines @@
     // CompositorObservers to be notified before starting another
     // draw cycle.
     ScheduleDraw();
   }
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingEnded(this));
 }
 
 }  // namespace ui