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

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index fdfb54c56eba9160757c38517779f1cdc369ab61..8da7b0433d8399ef790c7065c53a414e8e416ab4 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -1448,7 +1448,16 @@ 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(