Make sure observers are not nullptr

base/observer_list.h

Index: base/observer_list.h
diff --git a/base/observer_list.h b/base/observer_list.h
index f7b92679e9e37af4d3c6d6492da93aed9789cd4e..e473b3250ae58dedc74c1801a500bafe27f377b9 100644
--- a/base/observer_list.h
+++ b/base/observer_list.h
@@ -154,6 +154,7 @@ ObserverType* ObserverListBase<ObserverType>::Iterator::GetNext() {
 
 template <class ObserverType>
 void ObserverListBase<ObserverType>::AddObserver(ObserverType* obs) {
+  DCHECK(obs);

[oshima, 2015/04/03 23:09:28]

This will most likely lead to crash, so maybe we want CHECK instead?

(andi'll revert the change in widget)

[danakj, 2015/04/06 17:18:47]

DCHECK is right. You can CHECK with a TODO and bug to put it back to a DCHECK if
you want to, to track down a bug. But it should be a DCHECK in the long term.

   if (std::find(observers_.begin(), observers_.end(), obs)
       != observers_.end()) {
     NOTREACHED() << "Observers can only be added once!";
@@ -164,6 +165,7 @@ void ObserverListBase<ObserverType>::AddObserver(ObserverType* obs) {
 
 template <class ObserverType>
 void ObserverListBase<ObserverType>::RemoveObserver(ObserverType* obs) {
+  DCHECK(obs);

[danakj, 2015/04/06 17:18:47]

do we care about removing null? we don't seem to care about removing things not
in the list.

   typename ListType::iterator it =
     std::find(observers_.begin(), observers_.end(), obs);
   if (it != observers_.end()) {