Layout transitions triggered on key-down instead of key-up.

ui/keyboard/resources/elements/kb-key.html

 <!--
   -- Copyright 2013 The Chromium Authors. All rights reserved.
   -- Use of this source code is governed by a BSD-style license that can be
   -- found in the LICENSE file.
   -->
 
 <polymer-element name="kb-key" extends="kb-key-base"
     attributes="keyCode shiftModifier weight">
   <template>
     <style>
@@ skipping 42 matching lines @@
       },
     });
   </script>
 </polymer-element>
 
 <!-- Special keys -->
 
 <polymer-element name="kb-shift-key" attributes="unlockedCase lockedCase"
     class="shift dark" char="Shift" extends="kb-key">
   <script>
-    Polymer('kb-shift-key', {
-       /**
-        * Defines how capslock effects keyset transition. We always transition
-        * from the unlockedCase to the lockedCase if capslock is on.
-        * @type {string}
-        */
-      unlockedCase: 'lower',
-      lockedCase: 'upper',
 
-      down: function(event) {
-        this.super();
-        var detail = {};
-        if (this.keysetRules && this.keysetRules.dbl != undefined) {
-          detail.char = this.char || this.textContent;
-          detail.toKeyset = this.keysetRules.dbl[TO_KEYSET - OFFSET];
-          detail.nextKeyset = this.keysetRules.dbl[NEXT_KEYSET - OFFSET];
-        }
-        this.fire('enable-dbl', detail);
-        this.fire('enable-sel');
-      },
-    });
+    (function () {
+      /**
+       * Uses a closure to define one long press timer among all shift keys
+       * regardless of the layout they are in.
+       * @type {function}
+       */
+      var shiftLongPressTimer = undefined;
+
+      Polymer('kb-shift-key', {
+         /**
+          * Defines how capslock effects keyset transition. We always transition
+          * from the unlockedCase to the lockedCase if capslock is on.
+          * @type {string}
+          */
+        unlockedCase: 'lower',
+        lockedCase: 'upper',
+        control: true,
+
+        down: function(event) {
+          this.super();
+          var detail = {};
+          if (this.keysetRules && this.keysetRules.dbl != undefined) {
+            detail.char = this.char || this.textContent;
+            detail.toKeyset = this.keysetRules.dbl[TO_KEYSET - OFFSET];
+            detail.nextKeyset = this.keysetRules.dbl[NEXT_KEYSET - OFFSET];
+          }
+          this.fire('enable-dbl', detail);
+          this.fire('enable-sel');
+        },
+
+        /**
+         * Overrides longPressTimer for the shift key.
+         */
+        get longPressTimer() {
+          return shiftLongPressTimer;
+        },
+
+        set longPressTimer(timer) {
+          shiftLongPressTimer = timer;
+        },
+      });
+    })();
+
   </script>
 </polymer-element>
 
 <!--
   -- TODO(kevers): Display popup menu for selecting layout on keypress. Display
   -- code for keyboard layout in place of image.
   -->
 <polymer-element name="kb-layout-selector" class="layout-selector dark" char="Invalid"
     extends="kb-key">
   <script>
     Polymer('kb-layout-selector', {
       toLayout: 'qwerty'
     });
   </script>
 </polymer-element>