Added generated class level comments to all CSSPropertyAPIs.

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

 // Copyright 2016 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.
 
 #ifndef {{api_classname}}_h
 #define {{api_classname}}_h
 
 #include "core/CSSPropertyNames.h"
 #include "core/css/properties/CSSPropertyAPI.h"
 
 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 %}
   static {{all_api_methods[api_method].return_type}} {{api_method}}{{all_api_methods[api_method].parameters}};
   {% endfor %}
 };
 
 }  // namespace blink
 
 #endif  // {{api_classname}}_h