Make customElements.define faster

third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CustomElementDefinition_h
 #define CustomElementDefinition_h
 
 #include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/ScriptWrappable.h"  // For TraceWrapperBase
 #include "core/CoreExport.h"
 #include "core/dom/custom/CustomElementDescriptor.h"
 #include "platform/heap/Handle.h"
 #include "platform/wtf/HashSet.h"
 #include "platform/wtf/Noncopyable.h"
 #include "platform/wtf/text/AtomicString.h"
 #include "platform/wtf/text/AtomicStringHash.h"
 
 namespace blink {
 
 class Document;
 class Element;
 class ExceptionState;
 class HTMLElement;
 class QualifiedName;
 
 class CORE_EXPORT CustomElementDefinition
-    : public GarbageCollectedFinalized<CustomElementDefinition> {
+    : public GarbageCollectedFinalized<CustomElementDefinition>,
+      public TraceWrapperBase {

[Michael Lippautz, 2017/04/19 08:49:12]

I don't see why this one should be traced. 

TraceWrapperBase means that the class itself doesn't have a wrapper assigned.
The trace wrappers method below also doesn't trace any children. 

From a GC perspective this doesn't keep alive anything.

   WTF_MAKE_NONCOPYABLE(CustomElementDefinition);
 
  public:
+  // Each definition has an ID that is unique within the
+  // CustomElementRegistry that created it.
+  using Id = uint32_t;
+
   CustomElementDefinition(const CustomElementDescriptor&);
   CustomElementDefinition(const CustomElementDescriptor&,
                           const HashSet<AtomicString>&);
   virtual ~CustomElementDefinition();
 
   DECLARE_VIRTUAL_TRACE();
+  DECLARE_VIRTUAL_TRACE_WRAPPERS() {}
 
   const CustomElementDescriptor& Descriptor() { return descriptor_; }
 
-  // TODO(yosin): To support Web Modules, introduce an abstract
-  // class |CustomElementConstructor| to allow us to have JavaScript
-  // and C++ constructors and ask the binding layer to convert
-  // |CustomElementConstructor| to |ScriptValue|. Replace
-  // |getConstructorForScript()| by |getConstructor() ->
-  // CustomElementConstructor|.
   virtual ScriptValue GetConstructorForScript() = 0;
 
   using ConstructionStack = HeapVector<Member<Element>, 1>;
   ConstructionStack& GetConstructionStack() { return construction_stack_; }
 
   HTMLElement* CreateElementForConstructor(Document&);
   virtual HTMLElement* CreateElementSync(Document&, const QualifiedName&) = 0;
   HTMLElement* CreateElementAsync(Document&, const QualifiedName&);
 
   void Upgrade(Element*);
@@ skipping 52 matching lines @@
   ConstructionStack construction_stack_;
   HashSet<AtomicString> observed_attributes_;
   bool has_style_attribute_changed_callback_;
 
   void EnqueueAttributeChangedCallbackForAllAttributes(Element*);
 };
 
 }  // namespace blink
 
 #endif  // CustomElementDefinition_h