"Top Document Isolation" mode

content/common/site_isolation_policy.h

Index: content/common/site_isolation_policy.h
diff --git a/content/common/site_isolation_policy.h b/content/common/site_isolation_policy.h
index 5b1ee90b37f59daed519dac23360706f00458c59..ee556c39f112e9827d4184a3391ed3e6e3d7cef1 100644
--- a/content/common/site_isolation_policy.h
+++ b/content/common/site_isolation_policy.h
@@ -37,6 +37,10 @@ class CONTENT_EXPORT SiteIsolationPolicy {
   // Returns true if every site should be placed in a dedicated process.
   static bool UseDedicatedProcessesForAllSites();
 
+  // Returns true if third-party subframes of a page should be kept in a
+  // different process from the main frame.
+  static bool UseDedicatedProcessForTopDocument();

[Charlie Reis, 2016/03/18 21:15:13]

IsTopDocumentIsolationEnabled or something similar?  In the new approach, we
wouldn't actually be treating the top document as needing a dedicated process
(which is a smaller delta from Chrome's current process model).

+
   // Returns true if navigation and history code should maintain per-frame
   // navigation entries. This is an in-progress feature related to site
   // isolation, so the return value is currently tied to --site-per-process.