Add [CachedAccessor] attribute to cache (almost) constant accessors (window.document).

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

 /*
  * Copyright (C) 2008, 2009, 2011 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 47 matching lines @@
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/ScriptForbiddenScope.h"
 #include "platform/TraceEvent.h"
 #include "platform/heap/Handle.h"
 #include "platform/weborigin/SecurityOrigin.h"
 #include "public/platform/Platform.h"
 #include "wtf/Assertions.h"
 #include "wtf/StringExtras.h"
 #include "wtf/text/CString.h"
 #include <algorithm>
+#include <map>
 #include <utility>
 #include <v8-debug.h>
 #include <v8.h>
 
 namespace blink {
 
 static void checkDocumentWrapper(v8::Local<v8::Object> wrapper, Document* document)
 {
     ASSERT(V8Document::toImpl(wrapper) == document);
 }
@@ skipping 325 matching lines @@
     LocalFrame* frame = toLocalFrame(m_frame);
     v8::Local<v8::Value> documentWrapper = toV8(frame->document(), context->Global(), context->GetIsolate());
     if (documentWrapper.IsEmpty())
         return;
     ASSERT(documentWrapper == m_document.newLocal(m_isolate) || m_document.isEmpty());
     if (m_document.isEmpty())
         updateDocumentWrapper(v8::Local<v8::Object>::Cast(documentWrapper));
     checkDocumentWrapper(m_document.newLocal(m_isolate), frame->document());
 
     ASSERT(documentWrapper->IsObject());
-    // TODO(jochen): Don't replace the accessor with a data value. We need a way to tell v8 that the accessor's return value won't change after this point.
-    if (!v8CallBoolean(context->Global()->ForceSet(context, v8AtomicString(m_isolate, "document"), documentWrapper, static_cast<v8::PropertyAttribute>(v8::ReadOnly | v8::DontDelete))))
-        return;
+
+    // Update cache.
+    v8::Local<v8::Private> priv = cachedAccessors().at("Window#document").Get(m_isolate);

[Yuki, 2016/09/15 08:17:34]

Can you use V8PrivateProperty?

I think std::map and std::string are discouraged in Blink.

[Alfonso, 2016/09/16 14:21:48]

Done.

+
+    // TODO(peterssen): This should be probably constant.
+    // static_cast<v8::PropertyAttribute>(v8::ReadOnly | v8::DontDelete)
+    CHECK(context->Global()->ForceSet(context, v8::Private::AsSymbol(priv), documentWrapper).FromJust());

[jochen (gone - plz use gerrit), 2016/09/15 08:20:51]

why forceset?

[Alfonso, 2016/09/16 14:21:47]

Done.

 }
 
 void WindowProxy::updateActivityLogger()
 {
     m_scriptState->perContextData()->setActivityLogger(V8DOMActivityLogger::activityLogger(
         m_world->worldId(), m_frame->isLocalFrame() && toLocalFrame(m_frame)->document() ? toLocalFrame(m_frame)->document()->baseURI() : KURL()));
 }
 
 void WindowProxy::setSecurityToken(SecurityOrigin* origin)
 {
@@ skipping 127 matching lines @@
 }
 
 void WindowProxy::updateSecurityOrigin(SecurityOrigin* origin)
 {
     if (!isContextInitialized())
         return;
     setSecurityToken(origin);
 }
 
 } // namespace blink