Added api_methods flag to CSSProperties.json5.

third_party/WebKit/Source/core/css/properties/CSSPropertyAPI.h

 // 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 CSSPropertyAPI_h
 #define CSSPropertyAPI_h
 
 #include "core/CSSPropertyNames.h"
 #include "wtf/Allocator.h"
 
 namespace blink {
 
 class CSSValue;
 class CSSParserContext;
 class CSSParserTokenRange;
 
 // We will use this API to represent all functions used for property-specific
 // logic inside the blink style engine. All specific properties are subclasses
 // of CSSPropertyAPI.
 //
-// To add a new property using this API:
-// - Make a class that implements CSSPropertyAPI, and implement the static
-//   methods.
-// - Update the cssPropertyDescriptors array in CSSPropertyDescriptor.cpp to
-//   call GET_DESCRIPTOR(classname).
+// To add a new implementation of this API for a property:
+// - Make a class that implements CSSPropertyAPI.
+// - For each method that you wish to implement in this class, add this method
+//   name to the api_methods flag in CSSProperties.json5.
+// - Implement these methods in the .cpp file.
 //
-// To add new functions using this API:
-// - New functions and static variables can be added in this class. A default
-//   implementation of functions can optionally be provided.
-// - When adding new functions, also add them to GET_DESCRIPTOR, and the get()
-//   method in CSSPropertyDescriptors.cpp, and the descriptor struct in
-//   CSSPropertyDescriptor.h.
+// To add new functions to this API:
+// - Add the function to the struct below.
+// - Add the function to CSSPropertyAPIFiles.h.tmpl template file, surrounded
+//   with an {% if "methodName" in implementedMethods %} check.
+// - Add the function name to the valid_methods array in
+//   make_css_property_apis.py.
+// - Add function to the initializer list in the cssPropertyDescriptors array
+//   in CSSPropertyDescriptor.cpp.tmpl, and add a nullptr to the invalid
+//   CSSPropertyDescriptor.
 class CSSPropertyAPI {
   STATIC_ONLY(CSSPropertyAPI);
 
  public:
   // Parses a single CSS property and returns the corresponding CSSValue. If the
   // input is invalid it returns nullptr.
   static const CSSValue* parseSingleValue(CSSParserTokenRange&,
-                                          const CSSParserContext*);
+                                          const CSSParserContext*) {
+    NOTREACHED();
+    return nullptr;
+  }
 };
 
 }  // namespace blink
 
 #endif  // CSSPropertyAPI_h