[wrapper-tracing] Snapshot: Avoid adding non-Node wrappers to groups

third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 185 matching lines @@
         std::make_pair(new SuspendableObjectsInfo(m_foundV8Wrappers.size()),
                        std::move(m_foundV8Wrappers)));
   }
 
   // Trace through the blink heap to find all V8 wrappers reachable from any
   // of the collected roots. Also collect retainer edges on the way.
   void traceV8Roots() {
     for (auto& groupPair : m_nodesRequiringTracing) {
       v8::HeapProfiler::RetainerChildren groupChildren;
       for (auto& node : groupPair.second) {
-        auto wrappers = findV8WrappersDirectlyReachableFrom(node);
-        groupChildren.insert(wrappers.begin(), wrappers.end());
+        // Ignore the actual wrappers reachable as we only want to create
+        // groups of DOM nodes. The method is still used to collect edges
+        // though.
+        findV8WrappersDirectlyReachableFrom(node);

[haraken, 2017/01/24 21:04:58]

Now, isn't it useless to call findV8WrappersDirectlyReachableFrom?

+        groupChildren.insert(persistentForWrappable(node));
       }
       m_groups.push_back(std::make_pair(new RetainedDOMInfo(groupPair.first),
                                         std::move(groupChildren)));
     }
   }
 
   v8::HeapProfiler::RetainerEdges edges() { return std::move(m_edges); }
   v8::HeapProfiler::RetainerGroups groups() { return std::move(m_groups); }
 
   void markWrapper(const v8::PersistentBase<v8::Value>* value) const override {
     if (m_currentParent && m_currentParent != value)
       m_edges.push_back(std::make_pair(m_currentParent, value));
     m_foundV8Wrappers.insert(value);
   }
 
   void dispatchTraceWrappers(const TraceWrapperBase* traceable) const override {
     if (!m_onlyTraceSingleLevel || !traceable->isScriptWrappable() ||
         !reinterpret_cast<const ScriptWrappable*>(traceable)
              ->containsWrapper() ||
         !m_firstScriptWrappableTraced) {
       m_firstScriptWrappableTraced = true;
       traceable->traceWrappers(this);
     }
   }
 
  private:
+  inline v8::PersistentBase<v8::Value>* persistentForWrappable(
+      ScriptWrappable* wrappable) {
+    return &v8::Persistent<v8::Value>::Cast(*wrappable->rawMainWorldWrapper());
+  }
+
   v8::HeapProfiler::RetainerChildren findV8WrappersDirectlyReachableFrom(
       Node* traceable) {
     CHECK(m_foundV8Wrappers.empty());
     WTF::AutoReset<bool> scope(&m_onlyTraceSingleLevel, true);
     m_firstScriptWrappableTraced = false;
-    m_currentParent =
-        &v8::Persistent<v8::Value>::Cast(*traceable->rawMainWorldWrapper());
+    m_currentParent = persistentForWrappable(traceable);
 
     TracePrologue();
     traceable->wrapperTypeInfo()->traceWrappers(this, traceable);
     AdvanceTracing(
         0,
         v8::EmbedderHeapTracer::AdvanceTracingActions(
             v8::EmbedderHeapTracer::ForceCompletionAction::FORCE_COMPLETION));
     // Abort instead of Epilogue as we want to finish synchronously.
     AbortTracing();
 
@@ skipping 430 matching lines @@
   double startTime = WTF::currentTimeMS();
   v8::HandleScope scope(isolate);
   PendingActivityVisitor visitor(isolate, executionContext);
   toIsolate(executionContext)->VisitHandlesWithClassIds(&visitor);
   scanPendingActivityHistogram.count(
       static_cast<int>(WTF::currentTimeMS() - startTime));
   return visitor.pendingActivityFound();
 }
 
 }  // namespace blink