cros: Fix incorrect password dialog being immediately dismissed in tablet mode.

This repros by

  - Open login or lock screen, enter tablet mode
  - Type password using VK
  - Dismiss VK
  - Hit the submit button on the password field

You can also submit by hitting 'enter' on the VK

Bug: 892270
Change-Id: I39b40c6710a3ddca22cd110255f05014a9134798
Reviewed-on: https://chromium-review.googlesource.com/c/1287177Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601306}

ash/login/ui/login_bubble.cc

@@ -545,8 +545,15 @@ void LoginBubble::OnGestureEvent(ui::GestureEvent* event) {
 }
 
 void LoginBubble::OnKeyEvent(ui::KeyEvent* event) {
-  if (!bubble_view_ || event->type() != ui::ET_KEY_PRESSED)
+  // Ignore VKEY_PROCESSKEY; it is an IME event saying that the key has been
+  // processed. This event is also generated in tablet mode, ie, after
+  // submitting a password a VKEY_PROCESSKEY event is generated. If we treat
+  // that as a normal key event the password bubble will be dismissed
+  // immediately after submitting.
+  if (!bubble_view_ || event->type() != ui::ET_KEY_PRESSED ||
+      event->key_code() == ui::VKEY_PROCESSKEY) {
     return;
+  }
 
   // If current focus view is the button view, don't process the event here,
   // let the button logic handle the event and determine show/hide behavior.