Prevent AutoscrollForSelection when selecting text in a fixed-position element.

third_party/WebKit/LayoutTests/fast/events/autoscroll-disabled-in-fix.html

+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<div style="height: 400px; position: fixed; width: 400px; top: 500px;">
+<br />Fixed.......................
+<br />Fixed.......................
+<br />Fixed.......................
+<br />Fixed.......................
+<br />Fixed.......................
+<br />Fixed.......................
+<br />Fixed.......................
+</div>
+<div style="height: 2000px"></div>
+<script>
+var testFix = async_test('Selection-autoscroll should not be triggered when the selection is in a fixed-position element');
+testFix.step(function() {
+    if (!window.eventSender)
+        return;
+    document.body.offsetTop;

[bokan, 2016/10/24 13:22:00]

You shouldn't need this. If you're finding that layout hasn't occurred yet, you
can put all this inside a handler for the load event.

[sunyunjia, 2016/10/24 14:10:25]

Done.

+    var dragStartX = 50;
+    var dragStartY = 550;
+    var dragEndX = 60;
+    var dragMoveY = 580;
+    var dragEndY = 820;
+
+    eventSender.dragMode = false;
+    eventSender.mouseMoveTo(dragStartX, dragStartY);
+    eventSender.mouseDown();
+    eventSender.mouseMoveTo(dragEndX, dragMoveY);
+    eventSender.mouseMoveTo(dragEndX, dragEndY);
+
+    requestAnimationFrame(function() {
+        assert_equals(document.body.scrollTop, 0);
+        testFix.done();
+    });
+});
+</script>