Introduce "navigation target classification" for spatial navigation

Source/core/page/SpatialNavigation.h

 /*
  * Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Antonio Gomes <tonikitoo@webkit.org>
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 76 matching lines @@
 //
 // "Totally Aligned" elements are preferable candidates to move
 // focus to over "Partially Aligned" ones, that on its turns are
 // more preferable than "Not Aligned".
 enum RectsAlignment {
     None = 0,
     Partial,
     Full
 };
 
+// Classification of a focus candidate, ie. why a candidate is considered
+// "interesting" as a navigation target.
+enum NavigationClass {
+    NavigationClassNone,
+    NavigationClassFocusable,
+    NavigationClassFrameOwner,
+    NavigationClassScrollable,
+    NavigationClassEventHandler,
+};
+
 struct FocusCandidate {
     STACK_ALLOCATED();
 public:
     FocusCandidate()
         : visibleNode(nullptr)
         , focusableNode(nullptr)
         , enclosingScrollableBox(nullptr)
         , distance(maxDistance())
         , alignment(None)
         , isOffscreen(true)
         , isOffscreenAfterScrolling(true)
+        , targetClass(NavigationClassNone)
     {
     }
 
-    FocusCandidate(Node*, FocusType);
-    explicit FocusCandidate(HTMLAreaElement*, FocusType);
+    FocusCandidate(Node*, FocusType, NavigationClass);
     bool isNull() const { return !visibleNode; }
     bool inScrollableContainer() const { return visibleNode && enclosingScrollableBox; }
     bool isFrameOwnerElement() const { return visibleNode && visibleNode->isFrameOwnerElement(); }
     Document* document() const { return visibleNode ? &visibleNode->document() : nullptr; }
 
     // We handle differently visibleNode and FocusableNode to properly handle the areas of imagemaps,
     // where visibleNode would represent the image element and focusableNode would represent the area element.
     // In all other cases, visibleNode and focusableNode are one and the same.
     RawPtrWillBeMember<Node> visibleNode;
     RawPtrWillBeMember<Node> focusableNode;
     RawPtrWillBeMember<Node> enclosingScrollableBox;
     double distance;
     RectsAlignment alignment;
     LayoutRect rect;
     bool isOffscreen;
     bool isOffscreenAfterScrolling;
+    NavigationClass targetClass;
 };
 
 bool hasOffscreenRect(Node*, FocusType = FocusTypeNone);
 bool scrollInDirection(LocalFrame*, FocusType);
 bool scrollInDirection(Node* container, FocusType);
 bool canScrollInDirection(const Node* container, FocusType);
 bool canScrollInDirection(const LocalFrame*, FocusType);
 bool canBeScrolledIntoView(FocusType, const FocusCandidate&);
 bool areElementsOnSameLine(const FocusCandidate& firstCandidate, const FocusCandidate& secondCandidate);
 void distanceDataForNode(FocusType, const FocusCandidate& current, FocusCandidate&);
 Node* scrollableEnclosingBoxOrParentFrameForNodeInDirection(FocusType, Node*);
 LayoutRect nodeRectInAbsoluteCoordinates(Node*, bool ignoreBorder = false);
 LayoutRect frameRectInAbsoluteCoordinates(LocalFrame*);
 LayoutRect virtualRectForDirection(FocusType, const LayoutRect& startingRect, LayoutUnit width = 0);
 LayoutRect virtualRectForAreaElementAndDirection(HTMLAreaElement&, FocusType);
 HTMLFrameOwnerElement* frameOwnerElement(FocusCandidate&);
 
 } // namespace blink
 
 #endif // SpatialNavigation_h