Add SiteIsolation.IsolateExtensions metrics and tests.

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/lazy_instance.h"
@@ skipping 152 matching lines @@
   net::HttpCache* cache = request_context->GetURLRequestContext()->
       http_transaction_factory()->GetCache();
   if (cache)
     cache->OnExternalCacheHit(url, http_method);
 }
 
 // Helper function for retrieving all the sites in a frame tree.
 bool CollectSites(BrowserContext* context,
                   std::set<GURL>* sites,
                   FrameTreeNode* node) {
+  // Record about:blank as a real (process-having) site only if the SiteInstance
+  // is unassigned. Do not otherwise depend on the siteinstance's site URL,
+  // since its value reflects the current process model, and this function
+  // should behave identically across all process models.
+  if (node->current_url() == GURL(url::kAboutBlankURL) &&
+      node->current_frame_host()->GetSiteInstance()->HasSite()) {
+    return true;
+  }
   sites->insert(SiteInstance::GetSiteForURL(context, node->current_url()));
   return true;
 }
 
 bool FindMatchingProcess(int render_process_id,
                          bool* did_match_process,
                          FrameTreeNode* node) {
   if (node->current_frame_host()->GetProcess()->GetID() == render_process_id) {
     *did_match_process = true;
     return false;
@@ skipping 4438 matching lines @@
   return NULL;
 }
 
 void WebContentsImpl::SetForceDisableOverscrollContent(bool force_disable) {
   force_disable_overscroll_content_ = force_disable;
   if (view_)
     view_->SetOverscrollControllerEnabled(CanOverscrollContent());
 }
 
 }  // namespace content