Accessible scrollToMakeVisible should avoid scrolling if subfocus is visible.

Source/core/accessibility/AXObject.cpp

 /*
  * Copyright (C) 2008, 2009, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 691 matching lines @@
 // This may be out of range - the calling function should clip this
 // to the available range.
 static int computeBestScrollOffset(int currentScrollOffset, int subfocusMin, int subfocusMax, int objectMin, int objectMax, int viewportMin, int viewportMax)
 {
     int viewportSize = viewportMax - viewportMin;
 
     // If the object size is larger than the viewport size, consider
     // only a portion that's as large as the viewport, centering on
     // the subfocus as much as possible.
     if (objectMax - objectMin > viewportSize) {
-        // Subfocus must be within focus:
+        // Since it's impossible to fit the whole object in the
+        // viewport, exit now if the subfocus is already within the viewport.
+        if (subfocusMin - currentScrollOffset >= viewportMin
+            && subfocusMax - currentScrollOffset <= viewportMax)
+            return currentScrollOffset;
+
+        // Subfocus must be within focus.
         subfocusMin = std::max(subfocusMin, objectMin);
         subfocusMax = std::min(subfocusMax, objectMax);
 
         // Subfocus must be no larger than the viewport size; favor top/left.
         if (subfocusMax - subfocusMin > viewportSize)
             subfocusMax = subfocusMin + viewportSize;
 
         // Compute the size of an object centered on the subfocus, the size of the viewport.
         int centeredObjectMin = (subfocusMin + subfocusMax - viewportSize) / 2;
         int centeredObjectMax = centeredObjectMin + viewportSize;
@@ skipping 195 matching lines @@
         return ToggleButtonRole;
     if (ariaHasPopup())
         return PopUpButtonRole;
     // We don't contemplate RadioButtonRole, as it depends on the input
     // type.
 
     return ButtonRole;
 }
 
 } // namespace blink