bindings: Supports [LenientThis] extended attributes.

Source/bindings/core/v8/V8DOMConfiguration.cpp

Index: Source/bindings/core/v8/V8DOMConfiguration.cpp
diff --git a/Source/bindings/core/v8/V8DOMConfiguration.cpp b/Source/bindings/core/v8/V8DOMConfiguration.cpp
index 0cd625ba91c746f31caed20a4686da8daa33b095..ad487a8acca735300a0ec4bc8b706eb710bc32e7 100644
--- a/Source/bindings/core/v8/V8DOMConfiguration.cpp
+++ b/Source/bindings/core/v8/V8DOMConfiguration.cpp
@@ -102,6 +102,11 @@ void installAccessorInternal(v8::Isolate* isolate, v8::Local<ObjectOrTemplate> p
         if (accessor.setterForMainWorld)
             setterCallback = accessor.setterForMainWorld;
     }
+    // Support [LenientThis] by not specifying the signature.  V8 does not do
+    // the type checking against holder if no signature is specified.  Note that
+    // info.Holder() passed to callbacks will be *unsafe*.
+    if (accessor.holderCheckConfiguration == V8DOMConfiguration::DoNotCheckHolder)
+        signature = v8::Local<v8::Signature>();
     prototypeOrTemplate->SetAccessorProperty(
         v8AtomicString(isolate, accessor.name),
         functionOrTemplate(isolate, getterCallback, accessor.data, signature, 0, prototypeOrTemplate),