"Top Document Isolation" mode

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 5b169ba987df32d90d8d518458d663c99c954398..050902d23dd33b515f2f21b75581b99d8d1e8790 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -818,6 +818,10 @@ const char kTestingFixedHttpsPort[]         = "testing-fixed-https-port";
 // Type of the current test harness ("browser" or "ui").
 const char kTestType[]                      = "test-type";
 
+// Groups all out-of-process iframes to a different process from the process
+// of the top document. This is a performance isolation mode.
+const char kTopDocumentIsolation[] = "top-document-isolation";
+
 // Controls how text selection granularity changes when touch text selection
 // handles are dragged. Should be "character" or "direction". If not specified,
 // the platform default is used.