Investigate Android build problems in review 1414463004.

base/observer_list_threadsafe.h

Index: base/observer_list_threadsafe.h
diff --git a/base/observer_list_threadsafe.h b/base/observer_list_threadsafe.h
index e4204941949ff5996383b9906d916eca1322e85d..db4e6d2151ff2fa315604725e9a7657cb6caade7 100644
--- a/base/observer_list_threadsafe.h
+++ b/base/observer_list_threadsafe.h
@@ -111,11 +111,11 @@ class ObserverListThreadSafe
 
   // Add an observer to the list.  An observer should not be added to
   // the same list more than once.
-  void AddObserver(ObserverType* obs) {
+  bool AddObserver(ObserverType* obs) {
     // If there is not a current MessageLoop, it is impossible to notify on it,
     // so do not add the observer.
     if (!MessageLoop::current())
-      return;
+      return false;
 
     ObserverList<ObserverType>* list = nullptr;
     PlatformThreadId thread_id = PlatformThread::CurrentId();
@@ -126,6 +126,7 @@ class ObserverListThreadSafe
       list = &(observer_lists_[thread_id]->list);
     }
     list->AddObserver(obs);
+    return true;
   }
 
   // Remove an observer from the list if it is in the list.