MD History: Add spinners when new data is loading or searching

chrome/browser/resources/md_history/history_toolbar.js

Index: chrome/browser/resources/md_history/history_toolbar.js
diff --git a/chrome/browser/resources/md_history/history_toolbar.js b/chrome/browser/resources/md_history/history_toolbar.js
index 48189b8999f5a3216de51769244b42fd9844842c..fab7ba6d8ce211b4a14d0396784a8ebc481341a1 100644
--- a/chrome/browser/resources/md_history/history_toolbar.js
+++ b/chrome/browser/resources/md_history/history_toolbar.js
@@ -41,6 +41,12 @@ Polymer({
     searchTerm: {
       type: String,
       value: ''
+    },
+
+    // True if it's searching at the backend.
+    searching_: {

[tsergeant, 2016/04/18 01:26:36]

Nit: Rename this to `searching` with no underscore to show that it's a public
property.

(In javascript, we use an underscore at the end of a name to mark a method or
property as private).

[lshang, 2016/04/22 01:25:03]

Done.

+      type: Boolean,
+      value: false
     }
   },