Makes assert_selection() to set focus to sample IFRAME

third_party/WebKit/LayoutTests/editing/assert_selection.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
 // This file provides |assert_selection(sample, tester, expectedText)| assertion
 // to W3C test harness to write editing test cases easier.
 //
 // |sample| is an HTML fragment text which is inserted as |innerHTML|. It should
@@ skipping 536 matching lines @@
     document.body.appendChild(this.iframe_);
     /** @const @type {!HTMLDocument} */
     this.document_ = this.iframe_.contentDocument;
     /** @const @type {!Selection} */
     this.selection_ = this.iframe_.contentWindow.getSelection();
     this.selection_.document = this.document_;
     this.selection_.document.offsetLeft = this.iframe_.offsetLeft;
     this.selection_.document.offsetTop = this.iframe_.offsetTop;
     this.selection_.setClipboardData = setClipboardData;
 
+    // Set focus to sample IFRAME to make |eventSender| and
+    // |testRunner.execCommand()| to work on sample rather than main frame.
+    this.iframe_.focus();
     this.load(sampleText);
   }
 
   /** @return {!HTMLDocument} */
   get document() { return this.document_; }
 
   /** @return {!Selection} */
   get selection() { return this.selection_; }
 
   /**
@@ skipping 140 matching lines @@
   throw new Error(`${description}\n` +
     `\t expected ${expectedText},\n` +
     `\t but got  ${actualText},\n` +
     `\t sameupto ${commonPrefixOf(expectedText, actualText)}`);
 }
 
 // Export symbols
 window.Sample = Sample;
 window.assert_selection = assertSelection;
 })();