[SPv2] Introduce an option to output the GraphicsLayer tree as a flat layer list.

third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp

Index: third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp b/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
index c65fe69813019e2192353d116d99b82892ac5df0..b9154ad0b4eb4e92720a50673763c848e78cb9e1 100644
--- a/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/GraphicsLayer.cpp
@@ -607,10 +607,18 @@ static String pointerAsString(const void* ptr)
 std::unique_ptr<JSONObject> GraphicsLayer::layerTreeAsJSON(LayerTreeFlags flags) const
 {
     RenderingContextMap renderingContextMap;
+    if (flags & OutputChildrenAsLayerList) {
+        std::unique_ptr<JSONObject> json = JSONObject::create();
+        std::unique_ptr<JSONArray> layersArray = JSONArray::create();
+        for (auto& child : m_children)
+            child->layersAsJSONArray(flags, renderingContextMap, layersArray.get());
+        json->setArray("layers", std::move(layersArray));
+        return json;
+    }
     return layerTreeAsJSONInternal(flags, renderingContextMap);
 }
 
-std::unique_ptr<JSONObject> GraphicsLayer::layerTreeAsJSONInternal(LayerTreeFlags flags, RenderingContextMap& renderingContextMap) const
+std::unique_ptr<JSONObject> GraphicsLayer::layerAsJSONInternal(LayerTreeFlags flags, RenderingContextMap& renderingContextMap) const
 {
     std::unique_ptr<JSONObject> json = JSONObject::create();
 
@@ -714,6 +722,12 @@ std::unique_ptr<JSONObject> GraphicsLayer::layerTreeAsJSONInternal(LayerTreeFlag
         }
         json->setArray("squashingDisallowedReasons", std::move(squashingDisallowedReasonsJSON));
     }
+    return json;
+}
+
+std::unique_ptr<JSONObject> GraphicsLayer::layerTreeAsJSONInternal(LayerTreeFlags flags, RenderingContextMap& renderingContextMap) const
+{
+    std::unique_ptr<JSONObject> json = layerAsJSONInternal(flags, renderingContextMap);
 
     if (m_children.size()) {
         std::unique_ptr<JSONArray> childrenJSON = JSONArray::create();
@@ -725,6 +739,16 @@ std::unique_ptr<JSONObject> GraphicsLayer::layerTreeAsJSONInternal(LayerTreeFlag
     return json;
 }
 
+void GraphicsLayer::layersAsJSONArray(LayerTreeFlags flags, RenderingContextMap& renderingContextMap, JSONArray* jsonArray) const
+{
+    jsonArray->pushObject(layerAsJSONInternal(flags, renderingContextMap));
+
+    if (m_children.size()) {
+        for (auto& child : m_children)
+            child->layersAsJSONArray(flags, renderingContextMap, jsonArray);
+    }
+}
+
 String GraphicsLayer::layerTreeAsText(LayerTreeFlags flags) const
 {
     return layerTreeAsJSON(flags)->toPrettyJSONString();