IDL: Support optional union type arguments with default values

Source/bindings/scripts/idl_types.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 """IDL type handling.
 
 Classes:
 IdlTypeBase
  IdlType
  IdlUnionType
  IdlArrayOrSequenceType
@@ skipping 255 matching lines @@
             'member_types': self.member_types,
         }
 
     def __setstate__(self, state):
         self.member_types = state['member_types']
 
     @property
     def is_union_type(self):
         return True
 
+    def single_matching_member_type(self, predicate):
+        matching_types = filter(predicate, self.member_types)
+        if len(matching_types) > 1:
+            raise "%s is ambigious." % self.name
+        return matching_types[0] if matching_types else None
+
+    @property
+    def string_member_type(self):
+        return self.single_matching_member_type(
+            lambda member_type: (member_type.is_string_type or
+                                 member_type.is_enum))
+
+    @property
+    def numeric_member_type(self):
+        return self.single_matching_member_type(
+            lambda member_type: member_type.is_numeric_type)
+
+    @property
+    def boolean_member_type(self):
+        return self.single_matching_member_type(
+            lambda member_type: member_type.base_type == 'boolean')
+
     @property
     def as_union_type(self):
         # Note: Use this to "look through" a possible IdlNullableType wrapper.
         return self
 
     @property
     def name(self):
         """Return type name (or inner type name if nullable)
 
         http://heycam.github.io/webidl/#dfn-type-name
@@ skipping 87 matching lines @@
     def is_nullable(self):
         return True
 
     @property
     def name(self):
         return self.inner_type.name + 'OrNull'
 
     def resolve_typedefs(self, typedefs):
         self.inner_type = self.inner_type.resolve_typedefs(typedefs)
         return self