MD WebUI: Add loading spinner to cr-toolbar, hook into MD History toolbar

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

Index: ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
diff --git a/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js b/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
index 1729ff9d062bb8cb55020f9a0e78aa98efa59231..386925d0cc9ea577e81adfbc1f2030dbd0ac22e0 100644
--- a/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
+++ b/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
@@ -19,6 +19,13 @@ Polymer({
 
     // Tooltip to display on the clear search button.
     clearLabel: String,
+
+    // When true, show a loading spinner to indicate that the backend is
+    // processing the search. Will only show if the search field is open.
+    processing: {
+      type: Boolean,
+      reflectToAttribute: true
+    },
   },
 
   listeners: {
@@ -34,6 +41,10 @@ Polymer({
     return narrow ? 0 : -1;
   },
 
+  isSpinnerActive_: function(processing, showingSearch) {
+    return processing && showingSearch;
+  },
+
   /** @private */
   onInputBlur_: function() {
     if (!this.hasSearchText)