Move custom to dart conversion logic to IDLTypeInfo implementations.

lib/dom/scripts/systemnative.py

Index: lib/dom/scripts/systemnative.py
diff --git a/lib/dom/scripts/systemnative.py b/lib/dom/scripts/systemnative.py
index fe3bdfa99d8987e0e16477fb4cbf251043f07325..df58bbc4da7327d622a27daa64f0b81ee3961966 100644
--- a/lib/dom/scripts/systemnative.py
+++ b/lib/dom/scripts/systemnative.py
@@ -783,35 +783,13 @@ class NativeImplementationGenerator(systemwrapping.WrappingInterfaceGenerator):
       return_type_info = GetIDLTypeInfo(idl_return_type)
       self._cpp_impl_includes |= set(return_type_info.to_dart_includes())
 
-      # Generate C++ cast based on idl return type.
-      conversion_cast = return_type_info.conversion_cast('$FUNCTION_CALL')
-      if isinstance(return_type_info, SVGTearOffIDLTypeInfo):
-        svg_primitive_types = ['SVGAngle', 'SVGLength', 'SVGMatrix',
-            'SVGNumber', 'SVGPoint', 'SVGRect', 'SVGTransform']
-        conversion_cast = '%s::create($FUNCTION_CALL)'
-        if self._interface.id.startswith('SVGAnimated'):
-          conversion_cast = 'static_cast<%s*>($FUNCTION_CALL)'
-        elif return_type_info.idl_type() == 'SVGStringList':
-          conversion_cast = '%s::create(receiver, $FUNCTION_CALL)'
-        elif self._interface.id.endswith('List'):
-          conversion_cast = 'static_cast<%s*>($FUNCTION_CALL.get())'
-        elif return_type_info.idl_type() in svg_primitive_types:
-          conversion_cast = '%s::create($FUNCTION_CALL)'
-        else:
-          conversion_cast = 'static_cast<%s*>($FUNCTION_CALL)'
-        conversion_cast = conversion_cast % return_type_info.native_type()
-
       # Generate to Dart conversion of C++ value.
-      conversion_arguments = [conversion_cast]
-      if (return_type_info.idl_type() in ['DOMString', 'AtomicString'] and
-          'TreatReturnedNullStringAs' in attributes):
-        conversion_arguments.append('ConvertDefaultToNull')
-
+      to_dart_conversion = return_type_info.to_dart_conversion('$FUNCTION_CALL', self._interface.id, attributes)
       invocation_template = emitter.Format(
-          '        Dart_Handle returnValue = toDartValue($ARGUMENTS);\n'
+          '        Dart_Handle returnValue = $TO_DART_CONVERSION;\n'
           '        if (returnValue)\n'
           '            Dart_SetReturnValue(args, returnValue);\n',
-          ARGUMENTS=', '.join(conversion_arguments))
+          TO_DART_CONVERSION=to_dart_conversion)
 
     if raises_dom_exceptions:
       # Add 'ec' argument to WebCore invocation and convert DOM exception to Dart exception.