New WebContents created via ctrl-click should be in a new process.

content/browser/frame_host/navigator_impl.cc

 // Copyright 2013 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 "content/browser/frame_host/navigator_impl.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 753 matching lines @@
                        ui::PAGE_TRANSITION_LINK,
                        true /* is_renderer_initiated */);
   params.uses_post = uses_post;
   params.post_data = body;
   params.extra_headers = extra_headers;
   if (redirect_chain.size() > 0)
     params.redirect_chain = redirect_chain;
   params.should_replace_current_entry = should_replace_current_entry;
   params.user_gesture = user_gesture;
 
-  // RequestOpenURL is used only for local frames, so we can get here only if
-  // the navigation is initiated by a frame in the same SiteInstance as this
-  // frame.  Note that navigations on RenderFrameProxies do not use
-  // RequestOpenURL and go through RequestTransferURL instead.
-  params.source_site_instance = current_site_instance;

[Łukasz Anforowicz, 2017/02/09 16:53:01]

My initial fix was to never use params.source_site_instance in
CreateTargetContents in chrome/browser/ui/browser_navigator.cc, but this went
too far and broke hangouts when --isolate-extensions flag is present.

[alexmos, 2017/02/09 22:58:36]

Acknowledged.

-
   if (render_frame_host->web_ui()) {
     // Note that we hide the referrer for Web UI pages. We don't really want
     // web sites to see a referrer of "chrome://blah" (and some chrome: URLs
     // might have search terms or other stuff we don't want to send to the
     // site), so we send no referrer.
     params.referrer = Referrer();
 
     // Navigations in Web UI pages count as browser-initiated navigations.
     params.is_renderer_initiated = false;
   }
@@ skipping 490 matching lines @@
     if (navigation_handle)
       navigation_handle->update_entry_id_for_transfer(entry->GetUniqueID());
 
     controller_->SetPendingEntry(std::move(entry));
     if (delegate_)
       delegate_->NotifyChangedNavigationState(content::INVALIDATE_TYPE_URL);
   }
 }
 
 }  // namespace content