Add ListContainer::AppendByMoving

cc/base/list_container.h

Index: cc/base/list_container.h
diff --git a/cc/base/list_container.h b/cc/base/list_container.h
index 0c3772b82fdb9acbf27e731f42679025835f29ac..5463ca2066873bef445acb6a66bcbf084db2bb37 100644
--- a/cc/base/list_container.h
+++ b/cc/base/list_container.h
@@ -161,6 +161,8 @@ class CC_EXPORT ListContainerBase {
   size_t size() const;
   bool empty() const;
 
+  size_t MaxSizeForDerivedClass() const;
+
   // Unlike the ListContainer method, this one does not invoke element
   // destructors.
   void clear();
@@ -270,6 +272,7 @@ class ListContainer : public ListContainerBase {
   DerivedElementType* AllocateAndConstruct() {
     return new (Allocate(sizeof(DerivedElementType))) DerivedElementType;
   }
+
   // Take in derived element type and copy construct it at location generated by
   // Allocate().
   template <typename DerivedElementType>
@@ -277,6 +280,7 @@ class ListContainer : public ListContainerBase {
     return new (Allocate(sizeof(DerivedElementType)))
         DerivedElementType(*source);
   }
+
   // Construct a new element on top of an existing one.
   template <typename DerivedElementType>
   DerivedElementType* ReplaceExistingElement(Iterator at) {
@@ -284,6 +288,19 @@ class ListContainer : public ListContainerBase {
     return new (*at) DerivedElementType();
   }
 
+  // Appends a new item without copying. The original item will not be
+  // destructed and will be replaced with a new DerivedElementType. The
+  // DerivedElementType does not have to match the moved type as a full block
+  // of memory will be moved (up to MaxSizeForDerivedClass()).
+  template <typename DerivedElementType>
+  void AppendByMoving(DerivedElementType* item) {
+    size_t max_size_for_derived_class = MaxSizeForDerivedClass();
+    void* new_item = Allocate(max_size_for_derived_class);
+    memcpy(new_item, static_cast<void*>(item), max_size_for_derived_class);
+    // Construct a new element in-place so it can be destructed safely.
+    new (item) DerivedElementType;
+  }
+
   using ListContainerBase::size;
   using ListContainerBase::empty;