Bug 1310547 - Add removeAndGetNext/Previous methods to LinkedList (r=froydnj)

mfbt/LinkedList.h

@@ -250,6 +250,30 @@ public:
     Traits::exitList(this);
   }
 
+  /*
+   * Remove this element from the list containing it.  Returns a pointer to the
+   * element that follows this element (before it was removed).  This method
+   * asserts if the element does not belong to a list.
+   */
+  ClientType removeAndGetNext()
+  {
+    ClientType r = getNext();
+    remove();
+    return r;
+  }
+
+  /*
+   * Remove this element from the list containing it.  Returns a pointer to the
+   * previous element in the containing list (before the removal).  This method
+   * asserts if the element does not belong to a list.
+   */
+  ClientType removeAndGetPrevious()
+  {
+    ClientType r = getPrevious();
+    remove();
+    return r;
+  }
+
   /*
    * Identical to remove(), but also asserts in debug builds that this element
    * is in aList.

mfbt/tests/TestLinkedList.cpp

@@ -156,6 +156,24 @@ TestMove()
   list3.clear();
 }
 
+static void
+TestRemoveAndGet()
+{
+  LinkedList<SomeClass> list;
+
+  SomeClass one(1), two(2), three(3);
+  list.insertBack(&one);
+  list.insertBack(&two);
+  list.insertBack(&three);
+  { unsigned int check[] { 1, 2, 3 }; CheckListValues(list, check); }
+
+  MOZ_RELEASE_ASSERT(two.removeAndGetNext() == &three);
+  { unsigned int check[] { 1, 3 }; CheckListValues(list, check); }
+
+  MOZ_RELEASE_ASSERT(three.removeAndGetPrevious() == &one);
+  { unsigned int check[] { 1 }; CheckListValues(list, check); }
+}
+
 struct PrivateClass : private LinkedListElement<PrivateClass> {
   friend class mozilla::LinkedList<PrivateClass>;
   friend class mozilla::LinkedListElement<PrivateClass>;
@@ -244,6 +262,7 @@ main()
   TestList();
   TestPrivate();
   TestMove();
+  TestRemoveAndGet();
   TestRefPtrList();
   return 0;
 }