Treat zero-width collapsed borders as invisible

third_party/WebKit/Source/core/layout/CollapsedBorderValue.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 12 matching lines @@
  */
 
 #ifndef CollapsedBorderValue_h
 #define CollapsedBorderValue_h
 
 #include "core/style/BorderValue.h"
 #include "platform/wtf/Allocator.h"
 
 namespace blink {
 
+enum EBorderPrecedence {
+  kBorderPrecedenceOff,
+  kBorderPrecedenceTable,
+  kBorderPrecedenceColumnGroup,
+  kBorderPrecedenceColumn,
+  kBorderPrecedenceRowGroup,
+  kBorderPrecedenceRow,
+  kBorderPrecedenceCell
+};
+
 class CollapsedBorderValue {
   DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 
  public:
+  // Constructs a CollapsedBorderValue for non-existence border.
   CollapsedBorderValue()
       : color_(0),
         width_(0),
         style_(kBorderStyleNone),
         precedence_(kBorderPrecedenceOff),
         transparent_(false) {}
 
   CollapsedBorderValue(const BorderValue& border,
                        const Color& color,
                        EBorderPrecedence precedence)
       : color_(color),
         width_(border.NonZero() ? border.Width() : 0),
         style_(border.Style()),
         precedence_(precedence),
-        transparent_(border.IsTransparent()) {}
+        transparent_(border.IsTransparent()) {
+    DCHECK(precedence != kBorderPrecedenceOff);
+  }
 
   unsigned Width() const { return style_ > kBorderStyleHidden ? width_ : 0; }
   EBorderStyle Style() const { return static_cast<EBorderStyle>(style_); }
   bool Exists() const { return precedence_ != kBorderPrecedenceOff; }
   Color GetColor() const { return color_; }
   bool IsTransparent() const { return transparent_; }
   EBorderPrecedence Precedence() const {
     return static_cast<EBorderPrecedence>(precedence_);
   }
 
   bool IsSameIgnoringColor(const CollapsedBorderValue& o) const {
     return Width() == o.Width() && Style() == o.Style() &&
            Precedence() == o.Precedence();
   }
 
   bool VisuallyEquals(const CollapsedBorderValue& o) const {
     if (!IsVisible() && !o.IsVisible())
       return true;
     return GetColor() == o.GetColor() && IsTransparent() == o.IsTransparent() &&
            IsSameIgnoringColor(o);
   }
 
-  bool IsVisible() const {
-    return Style() > kBorderStyleHidden && !IsTransparent() && Exists();
-  }
+  bool IsVisible() const { return Width() && !IsTransparent(); }
 
   bool ShouldPaint(
       const CollapsedBorderValue& table_current_border_value) const {
     return IsVisible() && IsSameIgnoringColor(table_current_border_value);
   }
 
  private:
   Color color_;
   unsigned width_ : 24;
   unsigned style_ : 4;       // EBorderStyle
   unsigned precedence_ : 3;  // EBorderPrecedence
   unsigned transparent_ : 1;
 };
 
 }  // namespace blink
 
 #endif  // CollapsedBorderValue_h