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..cb31901cbaf348f5c2949c0db1662149c6618741 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();
@@ -283,6 +285,15 @@ class ListContainer : public ListContainerBase {
     at->~BaseElementType();
     return new (*at) DerivedElementType();
   }
+  // Appends a new item without copying. The original item will not be

[danakj, 2015/06/23 20:01:12]

nit: add whitespace above this

[pdr., 2015/06/23 21:42:42]

Done. I also added spaces to the 3 others above (ReplaceExistingElement,
AllocateAndCopyFrom, AllocateAndConstruct) for consistency.

+  // destructed and will be replaced with a new DerivedElementType.

[danakj, 2015/06/23 20:01:12]

Can you also mention that the DerivedElementType does not have to match the type
of the original item, since we will copy the full allocated block of bytes?

[pdr., 2015/06/23 21:42:41]

Done.

Comment now reads:
// 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* other_item) {
+    size_t max_size_for_derived_class = MaxSizeForDerivedClass();
+    void* new_item = Allocate(max_size_for_derived_class);
+    memcpy(new_item, (void*)other_item, max_size_for_derived_class);

[danakj, 2015/06/23 20:01:12]

why do you have to (void*)? and if so, use static_cast.

[pdr., 2015/06/23 21:42:41]

The c-style cats have been replaced with static_cats.

+    new (other_item) DerivedElementType;

[danakj, 2015/06/23 20:01:12]

can you leave a comment explaining this is overwriting the old memory with a new
DerivedElementType?

[pdr., 2015/06/23 21:42:42]

Done. The comment now reads:
// Construct a new element in-pace so it can be destructed safely.

+  }
 
   using ListContainerBase::size;
   using ListContainerBase::empty;