Pin keyboard improvements.

chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.html

 <!-- TODO(crbug.com/603217): Use i18n instead of string literals. Figure out
                              what i18n to use for keypad, ie, does 1 ABC make
                              sense in every scenario? -->
 
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
@@ skipping 202 matching lines @@
             <inner-text>$i18n{pinKeyboard9}</inner-text>
           </paper-button>
         </div>
         <div class="row keyboard bottom-row">
           <div class="digit-button"></div>
           <paper-button class="digit-button" on-tap="onNumberTap_" value="0">
             <inner-text>$i18n{pinKeyboard0}</inner-text>
           </paper-button>
           <paper-icon-button class="digit-button backspace-button"
                              disabled="[[!hasInput_(value)]]"
-                             on-tap="onPinClear_" icon="pin-keyboard:backspace">
+                             icon="pin-keyboard:backspace"
+                             on-mousedown="onBackspaceMouseDown_"
+                             on-mouseleave="onBackspaceMouseUpLeave_"
+                             on-mouseup="onBackspaceMouseUpLeave_">
           </paper-icon-button>
         </div>
       </div>
     </div>
   </template>
   <script src="pin_keyboard.js"></script>
 </dom-module>