Selection API: Do not change focus by Selection functions.

third_party/WebKit/LayoutTests/editing/selection/mixed-editability-7.html

 <p>This tests creating a selection based inside a nested editable region that extends out to editable content that is inside the same highest editable root.  'One' through 'Three' should be selected.</p>
 <div contenteditable="true">
 <div id="extent">One</div>
 <div contenteditable="false"><span>Two</span> <span id="base" contenteditable="true">Three</span></div>
 <div>Four</div>
 </div>
 
 <script>
 var base = document.getElementById("base");
 var extent = document.getElementById("extent");
+document.querySelector("div").focus();
 
 var sel = window.getSelection();
 sel.setBaseAndExtent(base, 1, extent, 0);
 </script>