Fixed some stylistic issues with <viewer-password-screen>

elements/viewer-password-screen/viewer-password-screen.html

 <polymer-element name="viewer-password-screen" attributes="text active">
 <template>
   <link rel="stylesheet" href="viewer-password-screen.css">
   <div class="center">
     <form class="form">
       <div id="message">{{text}}</div>
       <input id="password" type="password" size="20"></input>
       <input id="submit" type="submit" on-click={{submit}}></input>
       <div id="successMessage">{{successMessage}}</div>
     </form>
   </div>
 </template>
 <script>
   Polymer('viewer-password-screen', {
     text: 'This document is password protected. Please enter a password.',
     active: false,
     timerId: undefined,
     ready: function () {
-      // Prevent default form submit behavior from occuring.
-      this.$.submit.click = null;
-
       this.activeChanged();
     },
     accept: function() {
       this.successMessage = '&#x2714;'  // Tick.
       this.$.successMessage.style.color = 'rgb(0,125,0)';
       this.active = false;
     },
     deny: function() {
       this.successMessage = '&#x2718;';  // Cross.
       this.$.successMessage.style.color = 'rgb(255,0,0)';
       this.$.password.disabled = false;
       this.$.submit.disabled = false;
       this.$.password.focus();
       this.$.password.select();
     },
     submit: function(e) {
+      // Prevent the default form submission behavior.
       e.preventDefault();
       if (this.$.password.value.length == 0)
-        return false;
+        return;
       this.successMessage = '...';
       this.$.successMessage.style.color = 'rgb(0,0,0)';
       this.$.password.disabled = true;
       this.$.submit.disabled = true;
-      this.fire('password-submitted', { password: this.$.password.value });
-      return false;
+      this.fire('password-submitted', {password: this.$.password.value});
+      return;
     },
     activeChanged: function() {
       clearTimeout(this.timerId);
       this.timerId = undefined;
       if (this.active) {
         this.style.visibility = 'visible';
         this.style.opacity = 1;
         this.successMessage = '';
         this.$.password.focus();
       } else {
         this.style.opacity = 0;
         this.timerId = setTimeout(function() {
           this.style.visibility = 'hidden'
         }.bind(this), 400);
       }
     }
   });
 </script>
 </polymer-element>