Webview tag creation should be using storage partitions.

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 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/web_contents/web_contents_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
@@ skipping 378 matching lines @@
     WebContentsImpl* opener) {
   WebContentsImpl* new_contents = new WebContentsImpl(browser_context, opener);
 
   new_contents->Init(browser_context, site_instance, routing_id,
                      static_cast<const WebContentsImpl*>(base_web_contents));
   return new_contents;
 }
 
 WebContentsImpl* WebContentsImpl::CreateGuest(
     BrowserContext* browser_context,
-    const std::string& host_url,
+    SiteInstance* site_instance,
     int guest_instance_id,
     const BrowserPluginHostMsg_CreateGuest_Params& params) {
-  // The SiteInstance of a given guest is based on the fact that it's a guest
-  // in addition to which platform application the guest belongs to, rather
-  // than the URL that the guest is being navigated to.
-  GURL guest_site(
-      base::StringPrintf("%s://%s", chrome::kGuestScheme, host_url.c_str()));
-  SiteInstance* guest_site_instance =
-      SiteInstance::CreateForURL(browser_context, guest_site);
   WebContentsImpl* new_contents = WebContentsImpl::Create(
       browser_context,
-      guest_site_instance,
+      site_instance,
       MSG_ROUTING_NONE,
       NULL);  // base WebContents
   WebContentsImpl* new_contents_impl =
       static_cast<WebContentsImpl*>(new_contents);
 
   // This makes |new_contents| act as a guest.
   // For more info, see comment above class BrowserPluginGuest.
   new_contents_impl->browser_plugin_guest_.reset(
       BrowserPluginGuest::Create(
           guest_instance_id,
@@ skipping 2907 matching lines @@
 
 BrowserPluginGuest* WebContentsImpl::GetBrowserPluginGuest() {
   return browser_plugin_guest_.get();
 }
 
 BrowserPluginEmbedder* WebContentsImpl::GetBrowserPluginEmbedder() {
   return browser_plugin_embedder_.get();
 }
 
 }  // namespace content