Remove tabStop feature

Source/core/input/EventHandler.cpp

Index: Source/core/input/EventHandler.cpp
diff --git a/Source/core/input/EventHandler.cpp b/Source/core/input/EventHandler.cpp
index 5ce38751106f6d06f862f27b290b771cca457905..2385b4e685d715befd987ef797187d68381080ab 100644
--- a/Source/core/input/EventHandler.cpp
+++ b/Source/core/input/EventHandler.cpp
@@ -2069,8 +2069,6 @@ bool EventHandler::handleMouseFocus(const MouseEventWithHitTestResults& targeted
         // clear swallowEvent if the page already set it (e.g., by canceling
         // default behavior).
         if (element) {
-            if (slideFocusOnShadowHostIfNecessary(*element))
-                return true;
             if (!page->focusController().setFocusedElement(element, m_frame, WebFocusTypeMouse))
                 return true;
         } else {
@@ -2086,28 +2084,6 @@ bool EventHandler::handleMouseFocus(const MouseEventWithHitTestResults& targeted
     return false;
 }
 
-bool EventHandler::slideFocusOnShadowHostIfNecessary(const Element& element)
-{
-    if (element.shadowRoot() && !element.tabStop()) {
-        Document* doc = m_frame->document();
-        if (element.containsIncludingShadowDOM(doc->focusedElement())) {
-            // If the inner element is already focused, do nothing.
-            return true;
-        }
-
-        // If the host has a focusable inner element, focus it. Otherwise, the host takes focus.
-        Page* page = m_frame->page();
-        ASSERT(page);
-        Node* next = page->focusController().findFocusableNode(WebFocusTypeForward, *element.shadowRoot());
-        if (next && next->isElementNode() && element.containsIncludingShadowDOM(next)) {
-            // Use WebFocusTypeForward instead of WebFocusTypeMouse here to mean the focus has slided.
-            toElement(next)->focus(false, WebFocusTypeForward);
-            return true;
-        }
-    }
-    return false;
-}
-
 bool EventHandler::handleWheelEvent(const PlatformWheelEvent& event)
 {
 #define RETURN_WHEEL_EVENT_HANDLED() \