Disable the focus moves to an element which doesn't satisfy the spec.

Source/core/page/FocusController.cpp

Index: Source/core/page/FocusController.cpp
diff --git a/Source/core/page/FocusController.cpp b/Source/core/page/FocusController.cpp
index 149ff8a87bca01cdc267d43e738c6569f5615562..6ed173f09492a64f7a8c453c3e22a6f21caf978b 100644
--- a/Source/core/page/FocusController.cpp
+++ b/Source/core/page/FocusController.cpp
@@ -579,6 +579,7 @@ Node* FocusController::nextFocusableNode(FocusNavigationScope scope, Node* start
                 if (shouldVisit(node) && adjustedTabIndex(node) >= 0)
                     return node;
             }
+            return 0;

[hayato, 2014/08/25 06:52:16]

I am afraid we couldn't return 0 here.

Suppose we are given the following HTML:

<input id=A tabindex="1" type="text" />
<input id=B tabindex="-1" type="text" />
<input id=C tabindex="-1" type="text" />
<input id=D tabindex="-1" type="text" />

If users press 'Tab' key when the element 'B' is currently focused, I think the
element 'A' should be focused in this case.
If we return 0 here, the element A wouldn't get focused.

         }
 
         // First try to find a node with the same tabindex as start that comes after start in the scope.
@@ -626,6 +627,7 @@ Node* FocusController::previousFocusableNode(FocusNavigationScope scope, Node* s
             if (shouldVisit(node) && adjustedTabIndex(node) >= 0)
                 return node;
         }
+        return 0;

[hayato, 2014/08/25 06:52:16]

Ditto

     }
 
     if (Node* winner = findNodeWithExactTabIndex(startingNode, startingTabIndex, FocusTypeBackward))