1 files changed, 26 insertions, 4 deletions
diff --git a/chromium/base/callback_list.h b/chromium/base/callback_list.h
index d12a1e95baa..5b911fd4867 100644
--- a/chromium/base/callback_list.h
+++ b/chromium/base/callback_list.h
@@ -89,10 +89,13 @@ class CallbackListBase {
     }
 
     ~Subscription() {
-      if (list_->active_iterator_count_)
+      if (list_->active_iterator_count_) {
         iter_->Reset();
-      else
+      } else {
         list_->callbacks_.erase(iter_);
+        if (!list_->removal_callback_.is_null())
+          list_->removal_callback_.Run();
+      }
     }
 
    private:
@@ -111,6 +114,18 @@ class CallbackListBase {
         new Subscription(this, callbacks_.insert(callbacks_.end(), cb)));
   }
 
+  // Sets a callback which will be run when a subscription list is changed.
+  void set_removal_callback(const Closure& callback) {
+    removal_callback_ = callback;
+  }
+
+  // Returns true if there are no subscriptions. This is only valid to call when
+  // not looping through the list.
+  bool empty() {
+    DCHECK_EQ(0, active_iterator_count_);
+    return callbacks_.empty();
+  }
+
  protected:
   // An iterator class that can be used to access the list of callbacks.
   class Iterator {
@@ -167,17 +182,24 @@ class CallbackListBase {
   // iteration.
   void Compact() {
     typename std::list<CallbackType>::iterator it = callbacks_.begin();
+    bool updated = false;
     while (it != callbacks_.end()) {
-      if ((*it).is_null())
+      if ((*it).is_null()) {
+        updated = true;
         it = callbacks_.erase(it);
-      else
+      } else {
         ++it;
+      }
+
+      if (updated && !removal_callback_.is_null())
+        removal_callback_.Run();
     }
   }
 
  private:
   std::list<CallbackType> callbacks_;
   int active_iterator_count_;
+  Closure removal_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(CallbackListBase);
 };