Merge 117307 - Avoid jumpscroll when entering new text in a multi-line editor.

LayoutTests/editing/input/resources/reveal-utilities.js

 function offsetFromViewportTop(element)
 {
     return element.getClientRects()[0].top;
 }
 
 function offsetOfMiddleFromViewportTop(element)
 {
     return element.getClientRects()[0].top + Math.round(element.getClientRects()[0].height / 2);
 }
 
@@ skipping 46 matching lines @@
 }
 
 function performVerticalScrollingPasteTest()
 {
     copyText();
     if (performVerticalScrollingTest()) {
         document.execCommand("selectall");
         document.execCommand("paste");
     }
 }
+
+function performJumpAtTheEdgeTest(useCtrlKeyModifier)
+{
+    var textArea = document.getElementById("input");
+    textArea.focus();
+    if (window.eventSender) {
+        var previousScrollTop = 0, currentScrollTop = 0;
+        var jumpDetected = false;
+        for (var i = 0; i < 120; ++i) {
+            previousScrollTop = document.body.scrollTop;
+            eventSender.keyDown("\r", useCtrlKeyModifier ? ["ctrlKey"] : []);
+            currentScrollTop = document.body.scrollTop;
+            // Smooth scrolls are allowed.
+            if (Math.abs(previousScrollTop - currentScrollTop) > 24) {
+                jumpDetected = true;
+                break;
+            }
+        }
+        if (!jumpDetected)
+            document.write("PASS");
+        else
+            document.write("FAIL<br>Jump scroll from " + previousScrollTop + " to " + currentScrollTop);
+    }
+}