Add underlays and split off common overlay functionality

cc/quads/list_container.h

 // Copyright 2014 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 CC_QUADS_LIST_CONTAINER_H_
 #define CC_QUADS_LIST_CONTAINER_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
@@ skipping 191 matching lines @@
   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>
   DerivedElementType* AllocateAndCopyFrom(const DerivedElementType* source) {
     return new (Allocate(sizeof(DerivedElementType)))
         DerivedElementType(*source);
   }
+  // Construct a new element on top of an existing one.
+  template <typename DerivedElementType>
+  DerivedElementType* ReplaceExistingElement(Iterator at) {

[danakj, 2015/03/24 17:55:15]

Can you add unit tests for this method?

[achaulk, 2015/03/27 17:17:47]

Done.

+    at->~BaseElementType();
+    return new (*at) DerivedElementType();
+  }
 
   size_t size() const;
   bool empty() const;
   void clear();
 
   size_t AvailableSizeWithoutAnotherAllocationForTesting() const;
 
  private:
   // Hands out memory location for an element at the end of data structure.
   BaseElementType* Allocate(size_t size_of_actual_element_in_bytes);
 
   scoped_ptr<ListContainerCharAllocator> data_;
 
   DISALLOW_COPY_AND_ASSIGN(ListContainer);
 };
 
 #if !defined(COMPILER_MSVC)
 extern template class ListContainer<SharedQuadState>;
 extern template class ListContainer<DrawQuad>;
 #endif
 }  // namespace cc
 
 #endif  // CC_QUADS_LIST_CONTAINER_H_