Update from https://crrev.com/309717

base/observer_list_threadsafe.h

 // 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.
 
 #ifndef BASE_OBSERVER_LIST_THREADSAFE_H_
 #define BASE_OBSERVER_LIST_THREADSAFE_H_
 
 #include <algorithm>
 #include <map>
 
@@ skipping 149 matching lines @@
   void AssertEmpty() const {
     base::AutoLock lock(list_lock_);
     DCHECK(observer_lists_.empty());
   }
 
   // Notify methods.
   // Make a thread-safe callback to each Observer in the list.
   // Note, these calls are effectively asynchronous.  You cannot assume
   // that at the completion of the Notify call that all Observers have
   // been Notified.  The notification may still be pending delivery.
-  template <class Method>
-  void Notify(Method m) {
-    UnboundMethod<ObserverType, Method, Tuple0> method(m, MakeTuple());
-    Notify<Method, Tuple0>(method);
+  template <class Method, class... Params>
+  void Notify(Method m, const Params&... params) {
+    UnboundMethod<ObserverType, Method, Tuple<Params...>> method(
+        m, MakeTuple(params...));
+
+    base::AutoLock lock(list_lock_);
+    for (const auto& entry : observer_lists_) {
+      ObserverListContext* context = entry.second;
+      context->loop->PostTask(
+          FROM_HERE,
+          base::Bind(
+              &ObserverListThreadSafe<ObserverType>::template NotifyWrapper<
+                  Method, Tuple<Params...>>,
+              this, context, method));
+    }
   }
 
-  template <class Method, class A>
-  void Notify(Method m, const A& a) {
-    UnboundMethod<ObserverType, Method, Tuple1<A> > method(m, MakeTuple(a));
-    Notify<Method, Tuple1<A> >(method);
-  }
-
-  template <class Method, class A, class B>
-  void Notify(Method m, const A& a, const B& b) {
-    UnboundMethod<ObserverType, Method, Tuple2<A, B> > method(
-        m, MakeTuple(a, b));
-    Notify<Method, Tuple2<A, B> >(method);
-  }
-
-  template <class Method, class A, class B, class C>
-  void Notify(Method m, const A& a, const B& b, const C& c) {
-    UnboundMethod<ObserverType, Method, Tuple3<A, B, C> > method(
-        m, MakeTuple(a, b, c));
-    Notify<Method, Tuple3<A, B, C> >(method);
-  }
-
-  template <class Method, class A, class B, class C, class D>
-  void Notify(Method m, const A& a, const B& b, const C& c, const D& d) {
-    UnboundMethod<ObserverType, Method, Tuple4<A, B, C, D> > method(
-        m, MakeTuple(a, b, c, d));
-    Notify<Method, Tuple4<A, B, C, D> >(method);
-  }
-
-  // TODO(mbelshe):  Add more wrappers for Notify() with more arguments.
-
  private:
   // See comment above ObserverListThreadSafeTraits' definition.
   friend struct ObserverListThreadSafeTraits<ObserverType>;
 
   struct ObserverListContext {
     explicit ObserverListContext(NotificationType type)
         : loop(base::MessageLoopProxy::current()),
           list(type) {
     }
 
     scoped_refptr<base::MessageLoopProxy> loop;
     ObserverList<ObserverType> list;
 
     DISALLOW_COPY_AND_ASSIGN(ObserverListContext);
   };
 
   ~ObserverListThreadSafe() {
     STLDeleteValues(&observer_lists_);
   }
 
-  template <class Method, class Params>
-  void Notify(const UnboundMethod<ObserverType, Method, Params>& method) {
-    base::AutoLock lock(list_lock_);
-    typename ObserversListMap::iterator it;
-    for (it = observer_lists_.begin(); it != observer_lists_.end(); ++it) {
-      ObserverListContext* context = (*it).second;
-      context->loop->PostTask(
-          FROM_HERE,
-          base::Bind(&ObserverListThreadSafe<ObserverType>::
-              template NotifyWrapper<Method, Params>, this, context, method));
-    }
-  }
-
   // Wrapper which is called to fire the notifications for each thread's
   // ObserverList.  This function MUST be called on the thread which owns
   // the unsafe ObserverList.
   template <class Method, class Params>
   void NotifyWrapper(ObserverListContext* context,
       const UnboundMethod<ObserverType, Method, Params>& method) {
 
     // Check that this list still needs notifications.
     {
       base::AutoLock lock(list_lock_);
@@ skipping 38 matching lines @@
       ObserversListMap;
 
   mutable base::Lock list_lock_;  // Protects the observer_lists_.
   ObserversListMap observer_lists_;
   const NotificationType type_;
 
   DISALLOW_COPY_AND_ASSIGN(ObserverListThreadSafe);
 };
 
 #endif  // BASE_OBSERVER_LIST_THREADSAFE_H_