Links in PDF should be opened in new background tabs when ctrl + left clicked.

chrome/browser/pdf/pdf_extension_test.cc

 // Copyright 2014 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.
 
 #include <stddef.h>
 
 #include <vector>
 
 #include "base/base_paths.h"
 #include "base/files/file_enumerator.h"
@@ skipping 608 matching lines @@
       &y));
 
   gfx::Point point(x, y);
   content::WebContents* web_contents =
       browser()->tab_strip_model()->GetActiveWebContents();
 
   content::WindowedNotificationObserver observer(
       chrome::NOTIFICATION_TAB_ADDED,
       content::NotificationService::AllSources());
   content::SimulateMouseClickAt(web_contents, 0,
       blink::WebMouseEvent::ButtonMiddle, point);

[Lei Zhang, 2016/07/14 22:57:52]

Do you want to add another test for ctrl + left clicking? The two tests can
probably share the most of this function.

[jaepark, 2016/07/15 00:23:56]

Done.

   observer.Wait();
 
   int tab_count = browser()->tab_strip_model()->count();
   ASSERT_EQ(2, tab_count);
 
-  // TODO(jaepark): Middle mouse clicking on a link should not change
-  // the focus of the tab. See http://crbug.com/628054.
+  content::WebContents* active_web_contents =
+      browser()->tab_strip_model()->GetActiveWebContents();
+  ASSERT_EQ(web_contents, active_web_contents);
+
+
   content::WebContents* new_web_contents =
-      browser()->tab_strip_model()->GetActiveWebContents();
+      browser()->tab_strip_model()->GetWebContentsAt(1);
+  ASSERT_TRUE(new_web_contents);
   ASSERT_NE(web_contents, new_web_contents);
 
   const GURL& url = new_web_contents->GetURL();
   ASSERT_EQ(std::string("http://www.example.com/"), url.spec());
 }