Support window.opener after a process swap.

content/common/notification_type.h

Index: content/common/notification_type.h
diff --git a/content/common/notification_type.h b/content/common/notification_type.h
index 73b8d3302cc0ef3e5227a2c5b660b4ee1d5668fc..28b4ac8e1182e71d651b74738f8a050de27fbbc0 100644
--- a/content/common/notification_type.h
+++ b/content/common/notification_type.h
@@ -408,6 +408,11 @@ class NotificationType {
     // RenderProcessHost that corresponds to the process.
     RENDERER_PROCESS_TERMINATED,
 
+    // Indicates that a render process is starting to exit, such that it should
+    // not be used for future navigations.  The source will be the
+    // RenderProcessHost that corresponds to the process.
+    RENDERER_PROCESS_CLOSING,
+
     // Indicates that a render process was closed (meaning it exited, but the
     // RenderProcessHost might be reused).  The source will be the corresponding
     // RenderProcessHost.  The details will be a RendererClosedDetails struct.