Introduce support for origins that require process isolation.

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 3e70f6450bd01a111444c9f0c5f5ad651123f1b7..84d87a95d8ded80bc4bb3bbd074303a38433624b 100644
--- a/content/common/site_isolation_policy.h
+++ b/content/common/site_isolation_policy.h
@@ -41,6 +41,11 @@ class CONTENT_EXPORT SiteIsolationPolicy {
   // different process from the main frame.
   static bool IsTopDocumentIsolationEnabled();
 
+  // Returns true if there exist origins that require process isolation.  Such
+  // origins require a dedicated process, and hence they make cross-process
+  // iframes possible.
+  static bool AreIsolatedOriginsEnabled();
+
  private:
   SiteIsolationPolicy();  // Not instantiable.