Mojom: Blanket change to mark all pointer/handle fields as nullable.

ui/keyboard/webui/keyboard.mojom

Index: ui/keyboard/webui/keyboard.mojom
diff --git a/ui/keyboard/webui/keyboard.mojom b/ui/keyboard/webui/keyboard.mojom
index 9b05dc29fc119b3a537e99f264e02f89bb511b39..83e626beefc3dd664ec148c4a9b505f7ebe1566d 100644
--- a/ui/keyboard/webui/keyboard.mojom
+++ b/ui/keyboard/webui/keyboard.mojom
@@ -1,14 +1,14 @@
 [Client=KeyboardAPI]
 interface KeyboardUIHandlerMojo {
-  SendKeyEvent(string event_type,
+  SendKeyEvent(string? event_type,
                int32 char_value,
                int32 key_code,
-               string key_name,
+               string? key_name,
                int32 modifiers);
 
   HideKeyboard();
 };
 
 interface KeyboardAPI {
-  OnTextInputTypeChanged(string input_type);
+  OnTextInputTypeChanged(string? input_type);
 };