[ermine] Use meta-key only shortcut for toggling Overview.

Fixed: 36486

Change-Id: If4866069cd36fec5b97404ba8c69fa8c426b0a46
diff --git a/session_shells/ermine/shell/config/keyboard_shortcuts.json b/session_shells/ermine/shell/config/keyboard_shortcuts.json
index bdb8877..84e2ba4 100644
--- a/session_shells/ermine/shell/config/keyboard_shortcuts.json
+++ b/session_shells/ermine/shell/config/keyboard_shortcuts.json
@@ -22,9 +22,8 @@
   ],
   "overview": [
     {
-      "char": "space",
       "modifier": "meta",
-      "chord": "Meta + Space bar",
+      "chord": "Meta",
       "description": "Toggle Overview"
     }
   ],
diff --git a/session_shells/ermine/shell/lib/src/utils/keyboard_shortcuts.dart b/session_shells/ermine/shell/lib/src/utils/keyboard_shortcuts.dart
index 6b58760..b1535b9 100644
--- a/session_shells/ermine/shell/lib/src/utils/keyboard_shortcuts.dart
+++ b/session_shells/ermine/shell/lib/src/utils/keyboard_shortcuts.dart
@@ -9,7 +9,7 @@
 
 import 'package:fidl_fuchsia_ui_input2/fidl_async.dart';
 import 'package:fidl_fuchsia_ui_shortcut/fidl_async.dart' as ui_shortcut
-    show Registry, Shortcut, Listener, ListenerBinding;
+    show Registry, Shortcut, Trigger, Listener, ListenerBinding;
 import 'package:fidl_fuchsia_ui_views/fidl_async.dart' show ViewRef;
 import 'package:zircon/zircon.dart' show EventPairPair;
 
@@ -141,6 +141,9 @@
         super(
             id: ++lastId,
             key: Key.$valueOf(object['char']),
+            trigger: object['char'] == null && object['modifier'] != null
+                ? ui_shortcut.Trigger.keyPressedAndReleased
+                : null,
             modifiers: _modifiersFromArray(object['modifier']));
 
   @override