Add support for type checking of floating point attributes

Source/bindings/templates/attributes.cpp

 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 {% filter conditional(attribute.conditional_string) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(
 {%- if attribute.is_expose_js_accessors %}
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- else %}
 const v8::PropertyCallbackInfo<v8::Value>& info
 {%- endif %})
 {
@@ skipping 239 matching lines @@
     {% if attribute.idl_type == 'EventHandler' and interface_name == 'Window' %}
     if (!impl->document())
         return;
     {% endif %}
     {# Convert JS value to C++ value #}
     {% if attribute.idl_type != 'EventHandler' %}
     {{attribute.v8_value_to_local_cpp_value}};
     {% elif not is_node %}{# EventHandler hack #}
     moveEventListenerToNewWrapper(holder, {{attribute.event_handler_getter_expression}}, v8Value, {{v8_class}}::eventListenerCacheIndex, info.GetIsolate());
     {% endif %}
-    {% if attribute.enum_validation_expression %}
-    {# Setter ignores invalid enum values: http://www.w3.org/TR/WebIDL/#idl-enums #}
+    {# Type checking, possibly throw a TypeError, per:
+       http://www.w3.org/TR/WebIDL/#es-type-mapping #}
+    {% if attribute.has_type_checking_unrestricted %}
+    {# Non-finite floating point values (NaN, +Infinity or −Infinity), per:
+       http://heycam.github.io/webidl/#es-float
+       http://heycam.github.io/webidl/#es-double #}
+    if (!std::isfinite(cppValue)) {
+        exceptionState.throwTypeError("The provided {{attribute.idl_type}} value is non-finite.");
+        exceptionState.throwIfNeeded();
+        return;
+    }
+    {% elif attribute.enum_validation_expression %}
+    {# Setter ignores invalid enum values:
+       http://www.w3.org/TR/WebIDL/#idl-enums #}
     String string = cppValue;
     if (!({{attribute.enum_validation_expression}}))
         return;
     {% endif %}
     {# Pre-set context #}
     {% if attribute.is_custom_element_callbacks or
           (attribute.is_reflect and
            not(attribute.idl_type == 'DOMString' and is_node)) %}
     {# Skip on compact node DOMString getters #}
     CustomElementCallbackDispatcher::CallbackDeliveryScope deliveryScope;
@@ skipping 48 matching lines @@
     {% endif %}
     {% if attribute.has_custom_setter %}
     {{v8_class}}::{{attribute.name}}AttributeSetterCustom(v8Value, info);
     {% else %}
     {{cpp_class}}V8Internal::{{attribute.name}}AttributeSetter{{world_suffix}}(v8Value, info);
     {% endif %}
     TRACE_EVENT_SET_SAMPLING_STATE("V8", "V8Execution");
 }
 {% endfilter %}
 {% endmacro %}