IDL: Add IdlTypeBase.is_traceable

This is a follow-up CL of https://codereview.chromium.org/689013002

v8_union.py and v8_dictionary.py create a same flag from
the same condition. This should be a property of IdlType.

BUG=240176

Review URL: https://codereview.chromium.org/700603003

git-svn-id: svn://svn.chromium.org/blink/trunk@184814 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/bindings/scripts/v8_dictionary.py

@@ -141,8 +141,7 @@ def member_impl_context(member, interfaces_info, header_includes):
         'has_method_expression': has_method_expression(),
         'has_method_name': has_method_name_for_dictionary_member(member),
         'is_object': is_object,
-        'is_traceable': (idl_type.is_garbage_collected or
-                         idl_type.is_will_be_garbage_collected),
+        'is_traceable': idl_type.is_traceable,
         'member_cpp_type': member_cpp_type(),
         'rvalue_cpp_type': idl_type.cpp_type_args(used_as_rvalue_type=True),
         'setter_name': setter_name_for_dictionary_member(member),

third_party/WebKit/Source/bindings/scripts/v8_types.py

@@ -314,6 +314,13 @@ def gc_type(idl_type):
 IdlTypeBase.gc_type = property(gc_type)
 
 
+def is_traceable(idl_type):
+    return (idl_type.is_garbage_collected
+            or idl_type.is_will_be_garbage_collected)
+
+IdlTypeBase.is_traceable = property(is_traceable)
+
+
 ################################################################################
 # Includes
 ################################################################################

third_party/WebKit/Source/bindings/scripts/v8_union.py

@@ -84,8 +84,7 @@ def member_context(member, interfaces_info):
         'cpp_value_to_v8_value': member.cpp_value_to_v8_value(
             cpp_value='impl.getAs%s()' % member.name, isolate='isolate',
             creation_context='creationContext'),
-        'is_traceable': (member.is_garbage_collected or
-                         member.is_will_be_garbage_collected),
+        'is_traceable': member.is_traceable,
         'rvalue_cpp_type': member.cpp_type_args(used_as_rvalue_type=True),
         'specific_type_enum': 'SpecificType' + member.name,
         'type_name': member.name,