Added CSSPropertyAPI and CSS padding properties which implement this API

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 "core/css/CSSValue.h"
+#include "core/css/parser/CSSParserMode.h"
+#include "core/css/parser/CSSParserTokenRange.h"
+
+namespace blink {
+
+// 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 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.
+class CSSPropertyAPI {
+  STATIC_ONLY(CSSPropertyAPI);
+
+ public:
+  // A unique ID for the property.
+  // TODO(aazzam): Remove this once all callsites have been removed.
+  static const CSSPropertyID id;

[Z_DONOTUSE, 2016/12/08 01:00:18]

Can we give this a less inviting name so that only people who know what they're
doing use this? In particular, say what the id is for. temporaryIDForXXX or
something like that. I'm not quite following though, when will we be able to
stop storing IDs?

But, actually, I don't see anything that reads the id. Am I missing it?

[aazzam, 2016/12/08 02:27:10]

you're right, ID isn't read anywhere, I got rid of it :)

+
+  // 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&);
+};
+
+}  // namespace blink
+
+#endif  // CSSPropertyAPI_h