MD Settings: Add Learn More button to the Passwords subpage

chrome/browser/resources/settings/settings_page/settings_subpage.html

 <link rel="import" href="chrome://resources/html/polymer.html">
+<link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-resizable-behavior/iron-resizable-behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable-behavior.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-ripple/paper-ripple.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-spinner/paper-spinner.html">
 <link rel="import" href="../icons.html">
 <link rel="import" href="../route.html">
 <link rel="import" href="settings_subpage_search.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-subpage">
   <template>
     <style include="settings-shared">
       :host {
         --iron-icon-fill-color: var(--settings-nav-grey);
         display: block;
         padding-bottom: 60px;
       }
 
       .settings-box.first {
         min-height: 40px;
         padding-top: 8px;
       }
 
       .settings-box.first > h1 {
         -webkit-margin-start: 4px;
       }
 
+      #learnMore {
+        @apply(--cr-paper-icon-button-margin);
+        align-items: center;
+        display: flex;
+        height: var(--cr-icon-ripple-size);
+        justify-content: center;
+        position: relative;  /* Needed for paper-ripple. */
+        width: var(--cr-icon-ripple-size);
+      }
+
       paper-icon-button {
         /* Centers the ripple on the icon with appropriate margin on right. */
         -webkit-margin-end: 8px;
         -webkit-margin-start: -8px;
       }
 
       paper-spinner {
         @apply(--cr-icon-height-width);
       }
 
       h1 {
         color: var(--settings-nav-grey);
         flex: 1;  /* Push other items to the end. */
         font-size: 107.6923%;  /* Go to 14px from 13px */
         font-weight: 500;
       }
 
       settings-subpage-search {
-        -webkit-margin-start: auto;
+        /* Keep normal icon spacing from subpage-title-extra controls. */
+        -webkit-margin-start: 16px;
       }
     </style>
     <div class="settings-box first">
       <paper-icon-button icon="settings:arrow-back" on-tap="onTapBack_"
           aria-label="$i18n{back}">
       </paper-icon-button>
       <h1>[[pageTitle]]</h1>
+      <content select=".subpage-title-extra"></content>
+      <template is="dom-if" if="[[learnMoreUrl]]">
+        <a id="learnMore" aria-label="$i18n{learnMore}"
+            href="[[learnMoreUrl]]" target="_blank">
+          <iron-icon icon="settings:help-outline"></iron-icon>
+          <paper-ripple class="circle" center></paper-ripple>
+        </a>
+      </template>
       <template is="dom-if" if="[[searchLabel]]">
         <settings-subpage-search label="[[searchLabel]]"
             on-search-changed="onSearchChanged_">
         </settings-subpage-search>
       </template>
       <template is="dom-if" if="[[showSpinner]]">
-        <paper-spinner active></paper-spinner>          
+        <paper-spinner active></paper-spinner>
       </template>
-      <content select=".subpage-title-extra"></content>
     </div>
     <content></content>
   </template>
   <script src="settings_subpage.js"></script>
 </dom-module>