MD History: Added a clear browsing data button

chrome/browser/resources/md_history/history_toolbar.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.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/cr_elements/cr_search_field/cr_search_field.html">
 
 <dom-module id="history-toolbar">
   <template>
 
     <style>
       :host {
         background: rgb(63, 85, 102);
         color: #fff;
         height: 56px;
         transition: background-color 150ms;
       }
 
       :host,
       #items,
       #main-content {

[tsergeant, 2016/02/09 03:17:52]

Add #button-container and #toolbar-container to this and remove the identical
lines below.

[yingran, 2016/02/09 04:28:06]

Done.

         @apply(--layout-center);
         @apply(--layout-horizontal);
         width: 100%;
       }
 
       :host([items-selected_]) {
         background: rgb(68, 136, 255);
       }
 
       h1 {
@@ skipping 12 matching lines @@
         @apply(--layout-flex);
       }
 
       paper-icon-button {
         height: 36px;
         margin: 0 24px 0 2px;
         min-width: 36px;
         width: 36px;
       }
 
+      #clear-browsing-data {
+        flex: 1 1 960px;
+        max-width: 960px;
+      }
+
+      paper-button {
+        pointer-events: auto;
+      }
+
+      #button-container  {
+        @apply(--layout-horizontal);
+        @apply(--layout-center);
+        height: inherit;
+        left: 0;
+        pointer-events: none;
+        position: absolute;
+        top: 0;
+        width: 100%;
+      }
+
+      #toolbar-container {
+        @apply(--layout-horizontal);
+        @apply(--layout-center);
+        width: 100%;
+      }
+
+      #front-padding {
+        flex: 1 1 0;
+        min-width: 100px;
+      }
+
+      #back-padding {
+        flex: 1 1 0;
+      }
+
       [hidden] {
         display: none !important;
       }
     </style>
 
-    <div id="main-content" hidden$="{{itemsSelected_}}">
-      <h1 i18n-content="title" id="title"></h1>
-      <cr-search-field id="search-input"
-          i18n-values="label:search;clear-label:clearSearch"></cr-search-field>
+    <div id="toolbar-container">
+      <div id="main-content" hidden$="{{itemsSelected_}}">
+        <h1 i18n-content="title" id="title"></h1>
+        <cr-search-field id="search-input"
+            i18n-values="label:search;clear-label:clearSearch"></cr-search-field>
+      </div>
+
+      <div id="items" hidden$="{{!itemsSelected_}}">
+        <paper-icon-button icon="clear" id="cancel-icon-button"
+            on-tap="onClearSelectionTap_"></paper-icon-button>
+        <div id="number-selected">{{numberOfItemsSelected_(count)}}</div>
+        <paper-button id="cancel-button" on-tap="onClearSelectionTap_"
+            i18n-content="cancel"></paper-button>
+        <paper-button id="delete-button" i18n-content="delete"
+            on-tap="onDeleteTap_"></paper-button>
+      </div>
     </div>
 
-    <div id="items" hidden$="{{!itemsSelected_}}">
-      <paper-icon-button icon="clear" id="cancel-icon-button"
-          on-tap="onClearSelectionTap_"></paper-icon-button>
-      <div id="number-selected">{{numberOfItemsSelected_(count)}}</div>
-      <paper-button id="cancel-button" on-tap="onClearSelectionTap_"
-          i18n-content="cancel"></paper-button>
-      <paper-button id="delete-button" i18n-content="delete"
-          on-tap="onDeleteTap_"></paper-button>
+    <div id="button-container">
+      <div id="front-padding"></div>
+      <div id="clear-browsing-data" hidden$="{{itemsSelected_}}">

[tsergeant, 2016/02/09 03:17:52]

Maybe rename this div to something more generic, in case we want to add more
buttons here in the future?

How about

#centered-buttons ?

[yingran, 2016/02/09 04:28:06]

Done.

+        <paper-button on-tap="onClearBrowsingDataTap_"
+            i18n-content="clearBrowsingData"
+            id="clear-browsing-data-button">
+        </paper-button>
+      </div>
+      <div id="back-padding"></div>
     </div>
-
   </template>
   <script src="chrome://history/history_toolbar.js"></script>
 </dom-module>