Add wrapper container for a vector of OwnPtr<T>

cc/CCLayerTreeHostCommon.cpp

Index: cc/CCLayerTreeHostCommon.cpp
diff --git a/cc/CCLayerTreeHostCommon.cpp b/cc/CCLayerTreeHostCommon.cpp
index d60d43c0930631c4e7b40bcb53bf1ec85b11c05d..1b8b74d95e422d31be35eaecb1fb1590e0e59bac 100644
--- a/cc/CCLayerTreeHostCommon.cpp
+++ b/cc/CCLayerTreeHostCommon.cpp
@@ -635,7 +635,7 @@ static void calculateDrawTransformsInternal(LayerType* layer, LayerType* rootLay
 
     IntRect accumulatedDrawableContentRectOfChildren;
     for (size_t i = 0; i < layer->children().size(); ++i) {
-        LayerType* child = layer->children()[i].get();
+        LayerType* child = CCLayerTreeHostCommon::getChildAsRawPtr(layer->children(), i);
         IntRect drawableContentRectOfChildSubtree;
         calculateDrawTransformsInternal<LayerType, LayerList, RenderSurfaceType, LayerSorter>(child, rootLayer, sublayerMatrix, nextHierarchyMatrix, nextScrollCompensationMatrix,
                                                                                               clipRectForSubtree, subtreeShouldBeClipped, nearestAncestorThatMovesPixels,