[MD History] Focus the search bar on load.

ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-input/iron-input.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-input/paper-input-container.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-spinner/paper-spinner-lite.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_search_field/cr_search_field_behavior.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 
 <dom-module id="cr-toolbar-search-field">
   <template>
@@ skipping 72 matching lines @@
       /** Wide layout. */
       :host(:not([narrow])) {
         -webkit-padding-end: 0;
         background: rgba(0, 0, 0, 0.22);
         border-radius: 2px;
         cursor: text;
         width: var(--cr-toolbar-field-width);
       }
 
       :host(:not([narrow]):not([showing-search])) #icon,
-      :host(:not([narrow]):not([showing-search])) #prompt {
+      :host(:not([narrow])) #prompt {
         opacity: 0.6;
       }
 
       :host([narrow]:not([showing-search])) paper-input-container {
         display: none;
       }
 
       /* Search open. */
       :host([showing-search][spinner-active]) #icon {
         opacity: 0;
@@ skipping 28 matching lines @@
       <input is="iron-input" id="searchInput" type="search"
           on-blur="onInputBlur_" incremental></input>
     </paper-input-container>
     <paper-icon-button icon="cr:cancel" id="clearSearch"
         title="[[clearLabel]]" hidden$="[[!hasSearchText_]]"
         on-tap="hideSearch_">
     </paper-icon-button>
   </template>
   <script src="cr_toolbar_search_field.js"></script>
 </dom-module>