Makes descriptors hold nullptr for properties not implemented in API.

third_party/WebKit/Source/build/scripts/make_css_property_apis.py

Index: third_party/WebKit/Source/build/scripts/make_css_property_apis.py
diff --git a/third_party/WebKit/Source/build/scripts/make_css_property_apis.py b/third_party/WebKit/Source/build/scripts/make_css_property_apis.py
index bc21273f746b5db0fab280b4f03149891e0128ae..de909b5502d8a8c0b06286e505433709f89cd045 100755
--- a/third_party/WebKit/Source/build/scripts/make_css_property_apis.py
+++ b/third_party/WebKit/Source/build/scripts/make_css_property_apis.py
@@ -31,32 +31,36 @@ class CSSPropertyAPIWriter(make_style_builder.StyleBuilderWriter):
 
         # Temporary map of API classname to list of propertyIDs that the API class is for.
         properties_for_class = defaultdict(list)
+        # Temporary map of API classname to set of method names this API class implements
+        api_methods_for_class = defaultdict(set)
         for property in self._properties.values():
             if property['api_class'] is None:
                 continue
             classname = get_classname(property)
+            api_methods_for_class[classname] = property['api_methods']
             properties_for_class[classname].append(property['property_id'])
             self._outputs[classname + '.h'] = self.generate_property_api_h_builder(classname, property['api_methods'])
 
-        # Stores a list of classes with elements (index, classname, [propertyIDs, ..]).
+        # Stores a list of classes with elements (index, classname, [propertyIDs, ..], [api_methods, ...]).
         self._api_classes = []
 
-        ApiClass = namedtuple('ApiClass', ('index', 'classname', 'property_ids'))
+        ApiClass = namedtuple('ApiClass', ('index', 'classname', 'property_ids', 'api_methods'))
         for i, classname in enumerate(properties_for_class.keys()):
             self._api_classes.append(ApiClass(
                 index=i + 1,
                 classname=classname,
-                property_ids=properties_for_class[classname]
+                property_ids=properties_for_class[classname],
+                api_methods=api_methods_for_class[classname],
             ))
 
     @template_expander.use_jinja('CSSPropertyDescriptor.cpp.tmpl')
     def generate_property_descriptor_cpp(self):
         return {
             'api_classes': self._api_classes,
+            'api_methods': self.json5_file.parameters['api_methods']['valid_values'],
         }
 
     # Provides a function object given the classname of the property.
-    # This returned function generates a .h file for the specified property.
     def generate_property_api_h_builder(self, api_classname, api_methods):
         @template_expander.use_jinja('CSSPropertyAPIFiles.h.tmpl')
         def generate_property_api_h():