Do not create proxy hosts in the subtree of navigating frame.

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 <utility>
 
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 1379 matching lines @@
       proxy_hosts_.erase(iter);
     }
     RFHPendingDeleteMap::iterator pending_delete_iter =
         pending_delete_hosts_.find(old_site_instance_id);
     if (pending_delete_iter == pending_delete_hosts_.end() ||
         pending_delete_iter->second.get() != old_render_frame_host) {
       pending_delete_hosts_[old_site_instance_id] =
           linked_ptr<RenderFrameHostImpl>(old_render_frame_host.release());
     }
   } else {
-    CHECK(proxy_hosts_.find(render_frame_host_->GetSiteInstance()->GetId()) ==
-          proxy_hosts_.end());
+    // In --site-per-process, delete the proxy for the SiteInstance we are
+    // committing. In the case of main frame, the proxy wraps the
+    // |old_render_frame_host|, so it must be left intact.
+    // TODO(nasko): When committing into an existing process, the proxy
+    // should be swapped in the frame tree with the real frame, but this is
+    // not yet the case. Revisit this to ensure the necessary context is
+    // preserved.
+    if (CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kSitePerProcess) && !is_main_frame) {
+      RenderFrameProxyHostMap::iterator iter =
+          proxy_hosts_.find(render_frame_host_->GetSiteInstance()->GetId());
+      if (iter != proxy_hosts_.end()) {
+        delete iter->second;
+        proxy_hosts_.erase(iter);
+      }
+    }
 
     // Capture the active view count on the old RFH SiteInstance, since the
     // ownership might be passed into the proxy and the pointer will be
     // invalid.
     int active_view_count =
         static_cast<SiteInstanceImpl*>(old_render_frame_host->GetSiteInstance())
             ->active_view_count();
 
     if (is_main_frame) {
       RenderFrameProxyHostMap::iterator iter =
@@ skipping 14 matching lines @@
       // new process.
       if (!is_main_frame) {
         RenderFrameProxyHost* proxy = GetProxyToParent();
         if (proxy) {
           proxy->SetChildRWHView(
               render_frame_host_->render_view_host()->GetView());
         }
       }
     }
   }
+
+  // After all is done, there must never be a proxy in the list which has the
+  // same SiteInstance as the current RenderFrameHost.
+  CHECK(proxy_hosts_.find(render_frame_host_->GetSiteInstance()->GetId()) ==
+        proxy_hosts_.end());
 }
 
 void RenderFrameHostManager::ShutdownRenderFrameProxyHostsInSiteInstance(
     int32 site_instance_id) {
   // First remove any swapped out RFH for this SiteInstance from our own list.
   ClearProxiesInSiteInstance(site_instance_id, frame_tree_node_);
 
   // Use the safe RenderWidgetHost iterator for now to find all RenderViewHosts
   // in the SiteInstance, then tell their respective FrameTrees to remove all
   // RenderFrameProxyHosts corresponding to them.
@@ skipping 266 matching lines @@
 void RenderFrameHostManager::DeleteRenderFrameProxyHost(
     SiteInstance* instance) {
   RenderFrameProxyHostMap::iterator iter = proxy_hosts_.find(instance->GetId());
   if (iter != proxy_hosts_.end()) {
     delete iter->second;
     proxy_hosts_.erase(iter);
   }
 }
 
 }  // namespace content