bindings: Fixes [LenientThis] to refer to the correct object.

third_party/WebKit/Source/bindings/templates/attributes.cpp

Index: third_party/WebKit/Source/bindings/templates/attributes.cpp
diff --git a/third_party/WebKit/Source/bindings/templates/attributes.cpp b/third_party/WebKit/Source/bindings/templates/attributes.cpp
index e50f24a0b38506db6a76d696f8dfb639d028c6f4..b636f3d3c685f9b3c548f23feba1449583129e74 100644
--- a/third_party/WebKit/Source/bindings/templates/attributes.cpp
+++ b/third_party/WebKit/Source/bindings/templates/attributes.cpp
@@ -19,14 +19,11 @@ const v8::FunctionCallbackInfo<v8::Value>& info
     {# holder #}
     {% if not attribute.is_static %}
     {% if attribute.is_lenient_this %}
-    v8::Local<v8::Object> holder = {{v8_class}}::findInstanceInPrototypeChain(info.This(), info.GetIsolate());
-    if (holder.IsEmpty())
+    {# Make sure that info.Holder() really points to an instance if [LenientThis]. #}
+    if (!{{v8_class}}::hasInstance(info.Holder(), info.GetIsolate()))
         return; // Return silently because of [LenientThis].
-    // Note that it's okay to use |holder|, but |info.Holder()| is still unsafe
-    // and must not be used.
-    {% else %}
-    v8::Local<v8::Object> holder = info.Holder();
     {% endif %}
+    v8::Local<v8::Object> holder = info.Holder();
     {% endif %}
     {# impl #}
     {% if attribute.cached_attribute_validation_method %}
@@ -263,14 +260,11 @@ v8::Local<v8::Value> v8Value, const v8::FunctionCallbackInfo<v8::Value>& info
            not attribute.constructor_type) or
           raise_exception %}
     {% if attribute.is_lenient_this %}
-    v8::Local<v8::Object> holder = {{v8_class}}::findInstanceInPrototypeChain(info.This(), info.GetIsolate());
-    if (holder.IsEmpty())
+    {# Make sure that info.Holder() really points to an instance if [LenientThis]. #}
+    if (!{{v8_class}}::hasInstance(info.Holder(), info.GetIsolate()))
         return; // Return silently because of [LenientThis].
-    // Note that it's okay to use |holder|, but |info.Holder()| is still unsafe
-    // and must not be used.
-    {% else %}
-    v8::Local<v8::Object> holder = info.Holder();
     {% endif %}
+    v8::Local<v8::Object> holder = info.Holder();
     {% endif %}
     {% if raise_exception %}
     ExceptionState exceptionState(ExceptionState::SetterContext, "{{attribute.name}}", "{{interface_name}}", holder, info.GetIsolate());