Turn on AreCrossProcessFramesPossible by default.

content/browser/frame_host/render_frame_host_manager.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/render_frame_host_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <string>
@@ skipping 1080 matching lines @@
 
 bool RenderFrameHostManager::ShouldTransitionCrossSite() {
   // The logic below is weaker than "are all sites isolated" -- it asks instead,
   // "is any site isolated". That's appropriate here since we're just trying to
   // figure out if we're in any kind of site isolated mode, and in which case,
   // we ignore the kSingleProcess and kProcessPerTab settings.
   //
   // TODO(nick): Move all handling of kSingleProcess/kProcessPerTab into
   // SiteIsolationPolicy so we have a consistent behavior around the interaction
   // of the process model flags.
+  // TODO(creis): This looks like it will break --single-process and
+  // --process-per-tab.

[alexmos, 2017/02/04 02:03:01]

Filed https://bugs.chromium.org/p/chromium/issues/detail?id=688617.  It does
appear that we are currently breaking cross-process navigations under
--single-process if we are also in an OOPIF mode.

   if (SiteIsolationPolicy::AreCrossProcessFramesPossible())
     return true;
 
   // False in the single-process mode, as it makes RVHs to accumulate
   // in swapped_out_hosts_.
   // True if we are using process-per-site-instance (default) or
   // process-per-site (kProcessPerSite).
   // TODO(nick): Move handling of kSingleProcess and kProcessPerTab into
   // SiteIsolationPolicy.
   return !base::CommandLine::ForCurrentProcess()->HasSwitch(
@@ skipping 1668 matching lines @@
                                              resolved_url)) {
     DCHECK(!dest_instance ||
            dest_instance == render_frame_host_->GetSiteInstance());
     return false;
   }
 
   return true;
 }
 
 }  // namespace content