mash: Reverse the responsibilities of the NewWindowClient.

ash/public/interfaces/new_window.mojom

Index: ash/public/interfaces/new_window.mojom
diff --git a/ash/public/interfaces/new_window.mojom b/ash/public/interfaces/new_window.mojom
index 08a49f0c3a55ac24d76f9113d1b89c93cbc7eddc..7009400898069ed1f7b3b9423b957f0ae2b1c8c5 100644
--- a/ash/public/interfaces/new_window.mojom
+++ b/ash/public/interfaces/new_window.mojom
@@ -4,8 +4,13 @@
 
 module ash.mojom;
 
-// A delegate interface delegate to create or open windows that are not part of
-// ash.
+// An exported object in ash which lets an ash consumer set a client interface.
+interface NewWindowController {
+  SetClient(associated NewWindowClient client);
+};
+
+// A delegate interface that an ash user sends to ash to handle certain window
+// management responsibilities.
 interface NewWindowClient {
   // Invoked when the user uses Ctrl+T to open a new tab.
   NewTab();