[wrapper-tracing] Add heap snapshot generator infrastructure

third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h

Index: third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h b/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
index f64cdb08738cda741ad2e7ed522262a3a6f0f152..4be6a52788f3dc08dbd27ecd00e4662dd70f38b2 100644
--- a/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
+++ b/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
@@ -46,6 +46,7 @@ class CORE_EXPORT TraceWrapperBase {
 
  public:
   TraceWrapperBase() = default;
+  virtual bool isScriptWrappable() const { return false; }
 
   DECLARE_VIRTUAL_TRACE_WRAPPERS(){};
 };
@@ -62,6 +63,8 @@ class CORE_EXPORT ScriptWrappable : public TraceWrapperBase {
  public:
   ScriptWrappable() {}
 
+  bool isScriptWrappable() const override { return true; }
+
   template <typename T>
   T* toImpl() {
     // All ScriptWrappables are managed by the Blink GC heap; check that
@@ -166,6 +169,7 @@ class CORE_EXPORT ScriptWrappable : public TraceWrapperBase {
  private:
   // These classes are exceptionally allowed to use mainWorldWrapper().
   friend class DOMDataStore;
+  friend class HeapSnaphotWrapperVisitor;
   friend class V8HiddenValue;
   friend class V8PrivateProperty;
   friend class WebGLRenderingContextBase;
@@ -174,6 +178,13 @@ class CORE_EXPORT ScriptWrappable : public TraceWrapperBase {
     return v8::Local<v8::Object>::New(isolate, m_mainWorldWrapper);
   }
 
+  // Only use when really necessary, i.e., when passing over this
+  // ScriptWrappable's reference to V8. Should only be needed by GC
+  // infrastructure.
+  const v8::Persistent<v8::Object>* rawMainWorldWrapper() const {
+    return &m_mainWorldWrapper;
+  }
+
   v8::Persistent<v8::Object> m_mainWorldWrapper;
 };