Slimming Paint phase 2 compositing algorithm plumbing & skeleton display list API.

Source/platform/graphics/paint/DisplayItemTransformTreeBuilder.cpp

Index: Source/platform/graphics/paint/DisplayItemTransformTreeBuilder.cpp
diff --git a/Source/platform/graphics/paint/DisplayItemTransformTreeBuilder.cpp b/Source/platform/graphics/paint/DisplayItemTransformTreeBuilder.cpp
index f23c5182a0dfe7fbd6eba2d20b2bf819f4c7fd43..b56a702ee024665c492459bb7ea583fe81ae5eca 100644
--- a/Source/platform/graphics/paint/DisplayItemTransformTreeBuilder.cpp
+++ b/Source/platform/graphics/paint/DisplayItemTransformTreeBuilder.cpp
@@ -6,8 +6,10 @@
 #include "platform/graphics/paint/DisplayItemTransformTreeBuilder.h"
 
 #include "platform/graphics/paint/DisplayItem.h"
+#include "platform/graphics/paint/DisplayItemList.h"
 #include "platform/graphics/paint/DisplayItemTransformTree.h"
 #include "platform/graphics/paint/Transform3DDisplayItem.h"
+#include "public/platform/WebDisplayList.h"
 
 namespace blink {
 
@@ -56,6 +58,14 @@ static BeginDisplayItemClassification classifyBeginItem(const DisplayItem& begin
 
 } // namespace
 
+void DisplayItemTransformTreeBuilder::build(const DisplayItemList& displayList, const WebDisplayListDiff& displayListDiff)
+{
+    // TODO(chrishtr): use |displayListDiff| to optimize.
+    for (const auto& displayItem : displayList.displayItems()) {
+        processDisplayItem(*displayItem);
+    }
+}
+
 void DisplayItemTransformTreeBuilder::processDisplayItem(const DisplayItem& displayItem)
 {
     if (displayItem.isBegin()) {