Generate StyleBackgroundData in ComputedStyleBase.

This patch generates the following fields as part of a group:
- background ('storage_only' of type FillLayer)
- background_color ('storage_only' of type Color)

Since both fields correspond to shorthands, we specify them in
ComputedStyleExtraFields.json5.

All deleted code are correspondingly generated in
ComputedStyleBase, apart from the line

  background_data_(o.background_data_)

which is implicit in the compiler generated ComputedStyleBase
copy constructor.

Diff of generated files:
https://gist.github.com/darrnshn/c2d2e7f7429b6281987c8f1ff6e2c313/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2861623002
Cr-Commit-Position: refs/heads/master@{#469566}

third_party/WebKit/Source/core/css/ComputedStyleExtraFields.json5

@@ -169,5 +169,19 @@
       field_group: "surround",
       default_value: "BorderData()",
     },
+    {
+      name: "Background",
+      field_template: "storage_only",
+      field_type_path: "core/style/FillLayer",
+      default_value: "FillLayer(kBackgroundFillLayer, true)",
+      field_group: "background",
+    },
+    {
+      name: "BackgroundColor",
+      field_template: "storage_only",
+      field_type_path: "core/css/StyleColor",
+      default_value: "Color::kTransparent",
+      field_group: "background",
+    },
   ],
 }

third_party/WebKit/Source/core/style/ComputedStyle.cpp

@@ -116,7 +116,6 @@ ALWAYS_INLINE ComputedStyle::ComputedStyle()
     : ComputedStyleBase(), RefCounted<ComputedStyle>() {
   box_data_.Init();
   visual_data_.Init();
-  background_data_.Init();
   rare_non_inherited_data_.Init();
   rare_non_inherited_data_.Access()->deprecated_flexible_box_.Init();
   rare_non_inherited_data_.Access()->flexible_box_.Init();
@@ -138,7 +137,6 @@ ALWAYS_INLINE ComputedStyle::ComputedStyle(const ComputedStyle& o)
       RefCounted<ComputedStyle>(),
       box_data_(o.box_data_),
       visual_data_(o.visual_data_),
-      background_data_(o.background_data_),
       rare_non_inherited_data_(o.rare_non_inherited_data_),
       rare_inherited_data_(o.rare_inherited_data_),
       inherited_data_(o.inherited_data_),
@@ -333,7 +331,6 @@ void ComputedStyle::CopyNonInheritedFromCached(const ComputedStyle& other) {
   ComputedStyleBase::CopyNonInheritedFromCached(other);
   box_data_ = other.box_data_;
   visual_data_ = other.visual_data_;
-  background_data_ = other.background_data_;
   rare_non_inherited_data_ = other.rare_non_inherited_data_;
 
   // The flags are copied one-by-one because they contain
@@ -475,7 +472,6 @@ bool ComputedStyle::NonInheritedEqual(const ComputedStyle& other) const {
   return ComputedStyleBase::NonInheritedEqual(other) &&
          box_data_ == other.box_data_ &&
          visual_data_ == other.visual_data_ &&
-         background_data_ == other.background_data_ &&
          rare_non_inherited_data_ == other.rare_non_inherited_data_ &&
          svg_style_->NonInheritedEqual(*other.svg_style_);
 }

third_party/WebKit/Source/core/style/ComputedStyle.h

@@ -181,40 +181,10 @@ class CORE_EXPORT ComputedStyle : public ComputedStyleBase,
   friend class StyleResolverState;
   friend class StyleResolver;
 
- private:
-  class StyleBackgroundData : public RefCountedCopyable<StyleBackgroundData> {
-   public:
-    static PassRefPtr<StyleBackgroundData> Create() {
-      return AdoptRef(new StyleBackgroundData);
-    }
-    PassRefPtr<StyleBackgroundData> Copy() const {
-      return AdoptRef(new StyleBackgroundData(*this));
-    }
-
-    bool operator==(const StyleBackgroundData& other) const {
-      return background_ == other.background_ &&
-             background_color_ == other.background_color_;
-    }
-    bool operator!=(const StyleBackgroundData& other) const {
-      return !(*this == other);
-    }
-
-    FillLayer background_;
-    StyleColor background_color_;
-
-   private:
-    StyleBackgroundData()
-        : background_(FillLayer(kBackgroundFillLayer, true)),
-          background_color_(Color::kTransparent) {}
-
-    StyleBackgroundData(const StyleBackgroundData&) = default;
-  };
-
  protected:
   // non-inherited attributes
   DataRef<StyleBoxData> box_data_;
   DataRef<StyleVisualData> visual_data_;
-  DataRef<StyleBackgroundData> background_data_;
   DataRef<StyleRareNonInheritedData> rare_non_inherited_data_;
 
   // inherited attributes