Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

third_party/WebKit/Source/platform/graphics/paint/DisplayItemList.cpp

Index: third_party/WebKit/Source/platform/graphics/paint/DisplayItemList.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/DisplayItemList.cpp b/third_party/WebKit/Source/platform/graphics/paint/DisplayItemList.cpp
index a2030fb7c4bac6bc126726929ec7aadba9ee1ed9..84e0d961c05b766095791bf9d4ff1c34a18e12cb 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/DisplayItemList.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/DisplayItemList.cpp
@@ -4,6 +4,7 @@
 
 #include "platform/graphics/paint/DisplayItemList.h"
 
+#include "platform/graphics/LoggingCanvas.h"
 #include "platform/graphics/paint/DrawingDisplayItem.h"
 #include "platform/graphics/paint/PaintChunk.h"
 #include "third_party/skia/include/core/SkPictureAnalyzer.h"
@@ -48,4 +49,69 @@ DisplayItemList::itemsInPaintChunk(const PaintChunk& paintChunk) const {
                                begin() + paintChunk.endIndex);
 }
 
+std::unique_ptr<JSONArray> DisplayItemList::subsequenceAsJSON(
+    size_t beginIndex,
+    size_t endIndex,
+    bool showPictures,
+    bool skipNonDrawings) const {
+  std::unique_ptr<JSONArray> jsonArray = JSONArray::create();
+  size_t i = 0;
+  for (auto it = begin(); it != end(); ++it, ++i) {
+    std::unique_ptr<JSONObject> json = JSONObject::create();
+    if (i < beginIndex || i >= endIndex)
+      continue;
+
+    const DisplayItem& displayItem = *it;
+    if (skipNonDrawings && !displayItem.isDrawing())
+      continue;
+
+    if (!skipNonDrawings)
+      json->setInteger("index", i);
+#ifndef NDEBUG
+    StringBuilder stringBuilder;
+    displayItem.dumpPropertiesAsDebugString(stringBuilder);
+    json->setString("properties", stringBuilder.toString());
+#endif
+
+    if (displayItem.hasValidClient()) {
+#if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
+      if (!displayItem.client().isAlive()) {
+        json->setBoolean("clientIsAlive", true);
+      } else {
+#else
+      // debugName() and clientCacheIsValid() can only be called on a live
+      // client, so only output it for m_newDisplayItemList, in which we are
+      // sure the clients are all alive.
+      if (&list == &m_newDisplayItemList) {
+#endif
+#ifdef NDEBUG
+        json->setString(
+            "clientDebugName",
+            String::format("clientDebugName: \"%s\"",
+                           displayItem.client().debugName().ascii().data()));
+#endif
+      }
+#ifndef NDEBUG
+      if (showPictures && displayItem.isDrawing()) {
+        if (const SkPicture* picture =
+                static_cast<const DrawingDisplayItem&>(displayItem).picture()) {
+          json->setString("picture", pictureAsDebugString(picture));
+        }
+      }
+#endif
+    }
+    if (hasVisualRect(i)) {
+      IntRect localVisualRect = visualRect(i);
+      json->setString(
+          "visualRect",
+          String::format("[%d,%d %dx%d]", localVisualRect.x(),
+                         localVisualRect.y(), localVisualRect.width(),
+                         localVisualRect.height()));
+    }
+
+    jsonArray->pushObject(std::move(json));
+  }
+  return jsonArray;
+}
+
 }  // namespace blink