Add a readonly attribute to cr-input.

ui/webui/resources/cr_elements/cr_input/cr_input.html

 <link rel="import" href="chrome://resources/polymer/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/paper-input/paper-input-decorator.html">
 <link rel="import" href="chrome://resources/polymer/core-input/core-input.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_events/cr_events.html">
 
 <polymer-element name="cr-input">
   <template>
     <link rel="stylesheet" href="cr_input.css">
     <cr-events id="events"></cr-events>
 
     <!-- TODO(jlklein): Use 'autoValidate' instead of isInvalid binding when
          updated to 0.5.4. -->
     <paper-input-decorator id="decorator" label="{{label}}"
         floatingLabel="{{floatingLabel}}" value="{{value}}"
         disabled?="{{disabled}}" error="{{error}}"
         isInvalid="{{!$.input.validity.valid}}">
       <input is="core-input" id="input" value="{{value}}"
           committedValue="{{committedValue}}" disabled?="{{disabled}}"
-          required?="{{required}}" type="{{type}}">
+          required?="{{required}}" readonly?="{{readonly}}" type="{{type}}">

[Oren Blasberg, 2015/03/04 20:25:44]

Where does "readonly?" come from? When I search the polymer repo for core-input
for "readonly" I don't get any results.

I just want to understand how this wokrs.

     </paper-input-decorator>
   </template>
   <script src="cr_input.js"></script>
 </polymer-element>