Accessible scrollToMakeVisible should avoid scrolling if subfocus is visible.

Source/core/accessibility/AXObject.cpp

Index: Source/core/accessibility/AXObject.cpp
diff --git a/Source/core/accessibility/AXObject.cpp b/Source/core/accessibility/AXObject.cpp
index fdc942a5c53ca2774b7c5a8f44d26726cba6bf35..f431d9eed873402d3040b29a143268ae763a89b4 100644
--- a/Source/core/accessibility/AXObject.cpp
+++ b/Source/core/accessibility/AXObject.cpp
@@ -709,7 +709,13 @@ static int computeBestScrollOffset(int currentScrollOffset, int subfocusMin, int
     // 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);