Skip expensive hasInstance() type-checks in overloads

Source/bindings/templates/methods.cpp

Index: Source/bindings/templates/methods.cpp
diff --git a/Source/bindings/templates/methods.cpp b/Source/bindings/templates/methods.cpp
index 94b70730869b707916dfc76315938738c13565d4..5726897ac7e85f378979afc0deed61991a912242 100644
--- a/Source/bindings/templates/methods.cpp
+++ b/Source/bindings/templates/methods.cpp
@@ -1,7 +1,7 @@
 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
-static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
+static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info{% if method.overload_index %}, int typeCheckedArgumentIndex{% endif %})
 {
     {# Local variables #}
     {% if method.has_exception_state %}
@@ -172,7 +172,18 @@ if (!isUndefinedOrNull(info[{{argument.index}}]) && !info[{{argument.index}}]->I
 }
 {{argument.v8_value_to_local_cpp_value}};
 {% else %}{# argument.is_nullable #}
+{# Optionally do an "unsafe" type conversion if meaningful for this argument's
+   type and if this method is overloaded and the argument's type was checked as
+   part of overload resolution for this particular call. #}
+{% if argument.is_ever_distinguishing_argument and
+      argument.v8_value_to_local_cpp_value_without_type_check %}
+if (typeCheckedArgumentIndex == {{argument.index}})
+    {{argument.v8_value_to_local_cpp_value_without_type_check}};
+else
+    {{argument.v8_value_to_local_cpp_value}};
+{% else %}
 {{argument.v8_value_to_local_cpp_value}};
+{% endif %}
 {% endif %}{# argument.is_nullable #}
 {# Type checking, possibly throw a TypeError, per:
    http://www.w3.org/TR/WebIDL/#es-type-mapping #}
@@ -377,7 +388,7 @@ static void {{overloads.name}}Method{{world_suffix}}(const v8::FunctionCallbackI
     {# 10. If i = d, then: #}
     case {{length}}:
         {# Then resolve by testing argument #}
-        {% for test, method in tests_methods %}
+        {% for test, method, typed_checked_argument_index in tests_methods %}
         {% filter runtime_enabled(not overloads.runtime_enabled_function_all and
                                   method.runtime_enabled_function) %}
         if ({{test}}) {
@@ -387,7 +398,7 @@ static void {{overloads.name}}Method{{world_suffix}}(const v8::FunctionCallbackI
             {% if method.deprecate_as and not overloads.deprecate_all_as %}
             UseCounter::countDeprecation(callingExecutionContext(info.GetIsolate()), UseCounter::{{method.deprecate_as}});
             {% endif %}
-            {{method.name}}{{method.overload_index}}Method{{world_suffix}}(info);
+            {{method.name}}{{method.overload_index}}Method{{world_suffix}}(info, {{typed_checked_argument_index}});
             return;
         }
         {% endfilter %}
@@ -547,7 +558,7 @@ bool {{v8_class}}::PrivateScript::{{method.name}}Method({{method.argument_declar
 {% set name = '%sConstructorCallback' % v8_class
               if constructor.is_named_constructor else
               'constructor%s' % (constructor.overload_index or '') %}
-static void {{name}}(const v8::FunctionCallbackInfo<v8::Value>& info)
+static void {{name}}(const v8::FunctionCallbackInfo<v8::Value>& info{% if constructor.overload_index %}, int typeCheckedArgumentIndex{% endif %})
 {
     {% if constructor.is_named_constructor %}
     if (!info.IsConstructCall()) {