Disable top-document-isolation if the parent SiteInstance is a hosted app.

chrome/browser/chrome_content_browser_client.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 "chrome/browser/chrome_content_browser_client.h"
 
 #include <map>
 #include <set>
 #include <utility>
 #include <vector>
@@ skipping 1430 matching lines @@
 #if BUILDFLAG(ENABLE_EXTENSIONS)
   ChromeContentBrowserClientExtensionsPart::OverrideNavigationParams(
       site_instance, transition, is_renderer_initiated, referrer);
 #endif
 }
 
 bool ChromeContentBrowserClient::
     ShouldFrameShareParentSiteInstanceDespiteTopDocumentIsolation(
         const GURL& url,
         content::SiteInstance* parent_site_instance) {
-  return IsNTPSiteInstance(parent_site_instance);
+  if (IsNTPSiteInstance(parent_site_instance))
+    return true;
+
+#if BUILDFLAG(ENABLE_EXTENSIONS)
+  return ChromeContentBrowserClientExtensionsPart::
+      ShouldFrameShareParentSiteInstanceDespiteTopDocumentIsolation(
+          url, parent_site_instance);

[ncarter (slow), 2017/04/28 18:50:14]

(nit/optional) Might be better if factored like this:

#if BUILDFLAG(ENABLE_EXTENSIONS)
if (ChromeContentBrowserClientExtensionsPart::
       ShouldFrameShareParentSiteInstanceDespiteTopDocumentIsolation(
           url, parent_site_instance))
  return true;
#endif

return false;

+#else
+  return false;
+#endif
 }
 
 bool ChromeContentBrowserClient::IsSuitableHost(
     content::RenderProcessHost* process_host,
     const GURL& site_url) {
   Profile* profile =
       Profile::FromBrowserContext(process_host->GetBrowserContext());
   // This may be NULL during tests. In that case, just assume any site can
   // share any host.
   if (!profile)
@@ skipping 2153 matching lines @@
     RedirectNonUINonIOBrowserThreadsToTaskScheduler() {
   return variations::GetVariationParamValue(
              "BrowserScheduler", "RedirectNonUINonIOBrowserThreads") == "true";
 }
 
 // static
 void ChromeContentBrowserClient::SetDefaultQuotaSettingsForTesting(
     const storage::QuotaSettings* settings) {
   g_default_quota_settings = settings;
 }