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

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

Index: third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
index 6e8dbc7ca9c56d4b19ff438aa396fe8e1ff3c2c9..3c85f87abf4d887072ab97e29316642efc181fa9 100644
--- a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
@@ -65,6 +65,7 @@
 #include "wtf/StringExtras.h"
 #include "wtf/text/CString.h"
 #include <algorithm>
+#include <map>
 #include <utility>
 #include <v8-debug.h>
 #include <v8.h>
@@ -410,9 +411,13 @@ void WindowProxy::updateDocumentProperty()
     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()