Added CSSPropertyAPI and CSS padding properties which implement this API

Added the CSSPropertyAPI for a single method parseSingleValue. Made
CSSPaddingProperties which implements this API for a few css
properties. Added CSS property descriptor which uses a struct to store
function pointers for the property's functions.

BUG=668012

Review-Url: https://codereview.chromium.org/2533673002
Cr-Commit-Position: refs/heads/master@{#438057}

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

@@ -344,6 +344,11 @@ blink_core_sources("css") {
     "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",

third_party/WebKit/Source/core/css/parser/CSSPropertyParser.cpp

@@ -41,6 +41,7 @@
 #include "core/css/parser/CSSParserIdioms.h"
 #include "core/css/parser/CSSPropertyParserHelpers.h"
 #include "core/css/parser/CSSVariableParser.h"
+#include "core/css/properties/CSSPropertyDescriptor.h"
 #include "core/frame/UseCounter.h"
 #include "core/layout/LayoutTheme.h"
 #include "core/svg/SVGPathUtilities.h"
@@ -3465,6 +3466,17 @@ const CSSValue* CSSPropertyParser::parseSingleValue(
                                   m_range.peek().id());
     return consumeIdent(m_range);
   }
+
+  // Gets the parsing function for our current property from the property API.
+  // If it has been implemented, we call this function, otherwise we manually
+  // parse this value in the switch statement below. As we implement APIs for
+  // other properties, those properties will be taken out of the switch
+  // statement.
+  const CSSPropertyDescriptor& cssPropertyDesc =
+      CSSPropertyDescriptor::get(property);
+  if (cssPropertyDesc.temporaryCanReadValue)
+    return cssPropertyDesc.parseSingleValue(m_range, m_context);
+
   switch (property) {
     case CSSPropertyWillChange:
       return consumeWillChange(m_range);
@@ -3558,13 +3570,6 @@ const CSSValue* CSSPropertyParser::parseSingleValue(
       return consumeLengthOrPercent(m_range, m_context.mode(),
                                     ValueRangeNonNegative,
                                     UnitlessQuirk::Allow);
-    case CSSPropertyWebkitPaddingStart:
-    case CSSPropertyWebkitPaddingEnd:
-    case CSSPropertyWebkitPaddingBefore:
-    case CSSPropertyWebkitPaddingAfter:
-      return consumeLengthOrPercent(m_range, m_context.mode(),
-                                    ValueRangeNonNegative,
-                                    UnitlessQuirk::Forbid);
     case CSSPropertyClip:
       return consumeClip(m_range, m_context.mode());
     case CSSPropertyTouchAction:

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:
+  // 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

third_party/WebKit/Source/core/css/properties/CSSPropertyAPIPadding.cpp

+// 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.
+
+#include "core/css/properties/CSSPropertyAPIPadding.h"
+
+#include "core/css/parser/CSSParserTokenRange.h"
+#include "core/css/parser/CSSPropertyParserHelpers.h"
+
+namespace blink {
+
+const CSSValue* CSSPropertyAPIWebkitPadding::parseSingleValue(
+    CSSParserTokenRange& range,
+    const CSSParserContext& context) {
+  return consumeLengthOrPercent(
+      range, context.mode(), ValueRangeNonNegative,
+      CSSPropertyParserHelpers::UnitlessQuirk::Forbid);
+}
+
+}  // namespace blink

third_party/WebKit/Source/core/css/properties/CSSPropertyAPIPadding.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 CSSPropertyAPIPadding_h
+#define CSSPropertyAPIPadding_h
+
+#include "core/CSSPropertyNames.h"
+#include "core/css/properties/CSSPropertyAPI.h"
+
+namespace blink {
+
+// TODO(aazzam): Generate API .h files
+
+class CSSParserTokenRange;
+class CSSParserContext;
+
+class CSSPropertyAPIWebkitPadding : public CSSPropertyAPI {
+ public:
+  static const CSSValue* parseSingleValue(CSSParserTokenRange&,
+                                          const CSSParserContext&);
+};
+
+}  // namespace blink
+
+#endif  // CSSPropertyAPIPadding_h

third_party/WebKit/Source/core/css/properties/CSSPropertyDescriptor.cpp

+// 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.
+
+#include "core/css/properties/CSSPropertyDescriptor.h"
+
+#include "core/css/properties/CSSPropertyAPIPadding.h"
+
+namespace blink {
+
+// Initialises a CSSPropertyDescriptor. When functions are added to
+// CSSPropertyAPI, also add them to the struct initaliser below.
+#define GET_DESCRIPTOR(X) \
+  { X::parseSingleValue, true }
+
+// Initialises an invalid CSSPropertyDescriptor. When functions are added to
+// CSSPropertyAPI, add a nullptr to represent their function pointers in the
+// struct initaliser.
+#define GET_INVALID_DESCRIPTOR() \
+  { nullptr, false }
+
+static_assert(
+    std::is_pod<CSSPropertyDescriptor>::value,
+    "CSSPropertyDescriptor must be a POD to support using initializer lists.");
+
+static CSSPropertyDescriptor cssPropertyDescriptors[] = {
+    GET_INVALID_DESCRIPTOR(), GET_DESCRIPTOR(CSSPropertyAPIWebkitPadding),
+};
+
+const CSSPropertyDescriptor& CSSPropertyDescriptor::get(CSSPropertyID id) {
+  // TODO(aazzam): We are currently using hard-coded indexes for
+  // cssPropertyDescriptor since we have only implemented a few properties.
+  // Later, generate this switch statement, or alternatively return
+  // cssPropertyDescriptors[id], and generate the cssPropertyDescriptors array
+  // to hold invalid descriptors for methods which haven't been implemented yet.
+  switch (id) {
+    case CSSPropertyWebkitPaddingEnd:
+      return cssPropertyDescriptors[1];
+    case CSSPropertyWebkitPaddingStart:
+      return cssPropertyDescriptors[1];
+    case CSSPropertyWebkitPaddingBefore:
+      return cssPropertyDescriptors[1];
+    case CSSPropertyWebkitPaddingAfter:
+      return cssPropertyDescriptors[1];
+    default:
+      return cssPropertyDescriptors[0];
+  }
+}
+
+}  // namespace blink

third_party/WebKit/Source/core/css/properties/CSSPropertyDescriptor.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.
+
+#include "core/CSSPropertyNames.h"
+
+namespace blink {
+
+class CSSValue;
+class CSSParserTokenRange;
+class CSSParserContext;
+
+// Stores function pointers matching those declared in CSSPropertyAPI.
+struct CSSPropertyDescriptor {
+  const CSSValue* (*parseSingleValue)(CSSParserTokenRange&,
+                                      const CSSParserContext&);
+
+  // Stores whether or not this descriptor is for a valid property. Do not
+  // access the contents of this descriptor unless this value is true.
+  // TODO(aazzam): Remove this once the switch in
+  // CSSPropertyParser::parseSingleValue() has been completely replaced by
+  // CSSPropertyDescriptors.
+  bool temporaryCanReadValue;
+
+  // Returns the corresponding CSSPropertyDescriptor for a given CSSPropertyID.
+  // Use this function to access the API for a property. Returns a descriptor
+  // with isValid set to false if no descriptor exists for this ID.
+  static const CSSPropertyDescriptor& get(CSSPropertyID);
+};
+
+}  // namespace blink