Added generated class level comments to all CSSPropertyAPIs.

Added generated class level comments to all CSSPropertyAPIs with a
definition of the class and status.

BUG=668012

Review-Url: https://codereview.chromium.org/2864583002
Cr-Commit-Position: refs/heads/master@{#469580}

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

@@ -78,7 +78,7 @@ class CSSPropertyAPIWriter(StyleBuilderWriter):
             # This list contains duplicate entries, but is only used to check if a method is
             # implemented for an api_class.
             self.methods_for_classes[classname] += property_['api_methods']
-            self._outputs[classname + '.h'] = self.generate_property_api_h_builder(classname)
+            self._outputs[classname + '.h'] = self.generate_property_api_h_builder(classname, property_['name'])
 
         # Stores a list of classes with elements (index, classname, [propertyIDs, ..], [api_methods, ...]).
         self._api_classes = []
@@ -124,11 +124,12 @@ class CSSPropertyAPIWriter(StyleBuilderWriter):
         }
 
     # Provides a function object given the classname of the property.
-    def generate_property_api_h_builder(self, api_classname):
+    def generate_property_api_h_builder(self, api_classname, property_name):
         @template_expander.use_jinja('CSSPropertyAPIFiles.h.tmpl')
         def generate_property_api_h():
             return {
                 'api_classname': api_classname,
+                'property_name': property_name,
                 'methods_for_class': self.methods_for_classes[api_classname],
                 'all_api_methods': self.all_api_methods,
             }

third_party/WebKit/Source/build/scripts/templates/CSSPropertyAPIFiles.h.tmpl

@@ -13,6 +13,15 @@ namespace blink {
 class CSSParserTokenRange;
 class CSSParserContext;
 
+// {{api_classname}} is the API that contains logic
+// for handling the {{property_name}} property.
+// The methods defined here are standard among property APIs and can be
+// accessed through a CSSPropertyDescriptor object.
+//
+// Status (5th May 2017): Eventually, all logic pertaining to the
+// {{property_name}} property will be contained within
+// {{api_classname}}. Currently, the code base is in a transitional
+// state and property specific logic is still scattered around the code base.
 class {{api_classname}} : public CSSPropertyAPI {
  public:
   {% for api_method in all_api_methods if api_method in methods_for_class %}