Similar as extension, DOM UI needs to be created in its own process....

chrome/browser/browsing_instance.cc

 // Copyright (c) 2006-2008 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 "chrome/browser/browsing_instance.h"
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/renderer_host/site_instance.h"
@@ skipping 16 matching lines @@
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
   if (command_line.HasSwitch(switches::kProcessPerSite))
     return true;
 
   if (url.SchemeIs(chrome::kExtensionScheme)) {
     // Always consolidate extensions regardless of the command line, because
     // they will break if split into multiple processes.
     return true;
   }
 
+  if (url.SchemeIs(chrome::kChromeUIScheme)) {

[Charlie Reis, 2011/01/06 18:27:59]

I think we may have had a bug before-- should this use
DOMUIFactory::UseDOMUIForURL as we do in
RenderViewHostManager::ShouldSwapProcessesForNavigation?  (I think we want to
consolidate all types of DOMUI pages.)

Also, please add a trailing parenthesis to the comment below, as long as we're
here.

[klobag.chromium, 2011/01/06 20:23:02]

Done.

+    // Always consolidate instances of the new tab page (and instances of any
+    // other internal resource urls.
+    return true;
+  }
+
   if (!command_line.HasSwitch(switches::kProcessPerTab)) {
     // We are not in process-per-site or process-per-tab, so we must be in the
     // default (process-per-site-instance).  Only use the process-per-site
     // logic for particular sites that we want to consolidate.
     // Note that --single-process may have been specified, but that affects the
     // process creation logic in RenderProcessHost, so we do not need to worry
     // about it here.

[Charlie Reis, 2011/01/06 18:27:59]

This comment and the one below assume that the process-per-tab model didn't want
any tabs to be consolidated (since that was the original model).  That's no
longer the case-- we apparently want most of the special cases like extensions
and DOMUI to be consolidated whether we're in process-per-site-instance or
process-per-tab.

That means your change is correct, but please also move these comments up after
line 29 and update them accordingly.  We don't need the "if" on line 43 anymore.

[klobag.chromium, 2011/01/06 20:23:02]

Done.

[Charlie Reis, 2011/01/06 21:00:20]

Actually, it looks like the comments are gone now.  I think we still want them
above the extension check.

-    if (url.SchemeIs(chrome::kChromeUIScheme))
-      // Always consolidate instances of the new tab page (and instances of any
-      // other internal resource urls.
-      return true;
 
     // TODO(creis): List any other special cases that we want to limit to a
     // single process for all instances.
   }
 
   // In all other cases, don't use process-per-site logic.
   return false;
 }
 
 BrowsingInstance::SiteInstanceMap* BrowsingInstance::GetSiteInstanceMap(
@@ skipping 89 matching lines @@
     return true;
   }
   return false;
 }
 
 BrowsingInstance::~BrowsingInstance() {
   // We should only be deleted when all of the SiteInstances that refer to
   // us are gone.
   DCHECK(site_instance_map_.empty());
 }