Fix bug in ObserverListThreadsafe::RemoveObserver

Like ObserverList, ObserverListThreadSafe::RemoveObserver should do
nothing if the observer isn't in the list.  Instead, it causes weird
bugs if the list has 0 or 1 existing elements.

Add comments clarifying semantics of AddObserver/RemoveObserver.

Change AddObserver to do nothing in release mode if it tries to add an existing observer.

BUG=84922
TEST=


Review URL: http://codereview.chromium.org/7024037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@87944 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 9 insertions, 5 deletions

diff --git a/base/observer_list.h b/base/observer_list.h
index ca4b3fd..b8c2ae4 100644
--- a/base/observer_list.h
+++ b/base/observer_list.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -111,14 +111,18 @@ class ObserverListBase {
   explicit ObserverListBase(NotificationType type)
       : notify_depth_(0), type_(type) {}
 
-  // Add an observer to the list.
+  // Add an observer to the list.  An observer should not be added to
+  // the same list more than once.
   void AddObserver(ObserverType* obs) {
-    DCHECK(find(observers_.begin(), observers_.end(), obs) == observers_.end())
-        << "Observers can only be added once!";
+    if (std::find(observers_.begin(), observers_.end(), obs)
+        != observers_.end()) {
+      NOTREACHED() << "Observers can only be added once!";
+      return;
+    }
     observers_.push_back(obs);
   }
 
-  // Remove an observer from the list.
+  // Remove an observer from the list if it is in the list.
   void RemoveObserver(ObserverType* obs) {
     typename ListType::iterator it =
       std::find(observers_.begin(), observers_.end(), obs);