Check for already existing entry when adding to SiteProcessMap.

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 607 matching lines @@
 
   // When using --site-per-process, we notify the RFHM for all navigations,
   // not just main frame navigations.
   if (oopifs_possible) {
     FrameTreeNode* frame = render_frame_host->frame_tree_node();
     frame->render_manager()->DidNavigateFrame(
         render_frame_host, params.gesture == NavigationGestureUser);
   }
 
   // Update the site of the SiteInstance if it doesn't have one yet, unless
-  // assigning a site is not necessary for this URL.  In that case, the
-  // SiteInstance can still be considered unused until a navigation to a real
-  // page.
+  // assigning a site is not necessary for this URL or the commit was for an
+  // error page.  In that case, the SiteInstance can still be considered unused
+  // until a navigation to a real page.
   SiteInstanceImpl* site_instance = render_frame_host->GetSiteInstance();
-  if (!site_instance->HasSite() &&
-      ShouldAssignSiteForURL(params.url)) {
+  if (!site_instance->HasSite() && ShouldAssignSiteForURL(params.url) &&
+      !params.url_is_unreachable) {
     site_instance->SetSite(params.url);
   }
 
   // Need to update MIME type here because it's referred to in
   // UpdateNavigationCommands() called by RendererDidNavigate() to
   // determine whether or not to enable the encoding menu.
   // It's updated only for the main frame. For a subframe,
   // RenderView::UpdateURL does not set params.contents_mime_type.
   // (see http://code.google.com/p/chromium/issues/detail?id=2929 )
   // TODO(jungshik): Add a test for the encoding menu to avoid
@@ skipping 643 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