Make customElements.define faster

third_party/WebKit/Source/bindings/core/v8/V8PerContextData.h

Index: third_party/WebKit/Source/bindings/core/v8/V8PerContextData.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8PerContextData.h b/third_party/WebKit/Source/bindings/core/v8/V8PerContextData.h
index 8c3a550b3c16f45c893241f5ab777ceb6402295a..2ddc6c2a1a3a1dff757aaf3bdaa140a52bbb8fbb 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8PerContextData.h
+++ b/third_party/WebKit/Source/bindings/core/v8/V8PerContextData.h
@@ -112,6 +112,16 @@ class CORE_EXPORT V8PerContextData final {
   void ClearData(const char* key);
   Data* GetData(const char* key);
 
+  // Gets a Private to store custom element definition IDs on a
+  // function in use as a custom element constructor in this context.
+  v8::Local<v8::Private> GetPrivateCustomElementDefinitionId() {
+    if (UNLIKELY(private_custom_element_definition_id_.IsEmpty())) {
+      private_custom_element_definition_id_.Set(isolate_,
+                                                v8::Private::New(isolate_));
+    }
+    return private_custom_element_definition_id_.NewLocal(isolate_);
+  }
+
  private:
   V8PerContextData(v8::Local<v8::Context>);
 
@@ -135,6 +145,12 @@ class CORE_EXPORT V8PerContextData final {
   ScopedPersistent<v8::Context> context_;
   ScopedPersistent<v8::Value> error_prototype_;
 
+  // One function may be defined as a custom element constructor
+  // across multiple contexts simultaneously. Each context tags the
+  // constructor with a different Private to map the constructor back
+  // to its definition.
+  ScopedPersistent<v8::Private> private_custom_element_definition_id_;
+
   typedef Vector<std::unique_ptr<V0CustomElementBinding>>
       V0CustomElementBindingList;
   V0CustomElementBindingList custom_element_bindings_;