Added CSSPropertyAPI and CSS padding properties which implement this API

third_party/WebKit/Source/core/css/BUILD.gn

 # 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.
 
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("css") {
   split_count = 5
   sources = [
     "ActiveStyleSheets.cpp",
@@ skipping 324 matching lines @@
     "parser/CSSSupportsParser.cpp",
     "parser/CSSSupportsParser.h",
     "parser/CSSTokenizer.cpp",
     "parser/CSSTokenizerInputStream.cpp",
     "parser/CSSVariableParser.cpp",
     "parser/CSSVariableParser.h",
     "parser/MediaQueryBlockWatcher.cpp",
     "parser/MediaQueryParser.cpp",
     "parser/SizesAttributeParser.cpp",
     "parser/SizesCalcParser.cpp",
+    "properties/CSSPropertyAPI.h",
+    "properties/CSSPropertyAPIPadding.cpp",
+    "properties/CSSPropertyAPIPadding.h",
+    "properties/CSSPropertyDescriptor.cpp",
+    "properties/CSSPropertyDescriptor.h",
     "resolver/AnimatedStyleBuilder.cpp",
     "resolver/AnimatedStyleBuilder.h",
     "resolver/CSSToStyleMap.cpp",
     "resolver/CSSToStyleMap.h",
     "resolver/CSSVariableResolver.cpp",
     "resolver/CSSVariableResolver.h",
     "resolver/ElementResolveContext.cpp",
     "resolver/ElementResolveContext.h",
     "resolver/ElementStyleResources.cpp",
     "resolver/ElementStyleResources.h",
@@ skipping 31 matching lines @@
     "resolver/TransformBuilder.h",
     "resolver/ViewportStyleResolver.cpp",
     "resolver/ViewportStyleResolver.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }