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

third_party/WebKit/Source/bindings/core/v8/V8PrivateProperty.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V8PrivateProperty.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8PrivateProperty.cpp b/third_party/WebKit/Source/bindings/core/v8/V8PrivateProperty.cpp
index 4c555718f4377b3607bf6dacbc6cbf530c4f1360..3d03d7e3b480cb9dec086a12382b8fe6835e9e98 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8PrivateProperty.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8PrivateProperty.cpp
@@ -20,7 +20,7 @@ v8::Local<v8::Value> V8PrivateProperty::Symbol::getFromMainWorld(ScriptState* sc
 v8::Local<v8::Private> V8PrivateProperty::createV8Private(v8::Isolate* isolate, const char* symbol, size_t length)
 {
     v8::Local<v8::String> str = v8::String::NewFromOneByte(isolate, reinterpret_cast<const uint8_t*>(symbol), v8::NewStringType::kNormal, static_cast<int>(length)).ToLocalChecked();
-    return v8::Private::ForApi(isolate, str);
+    return v8::Private::New(isolate, str);

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

::ForApi is backed by another internal cache, so further ::ForApi calls with the
same name will reuse the same symbol. But since it's only used to initialize the
symbol once, ::New does the same.

Additionally, ::ForApi needs a context which is not yet created when
initializing 'window'. A window object is initialized and then the context is
created with it as global object.

 }
 
 } // namespace blink