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

chrome/browser/resources/md_history/history_list.js

Index: chrome/browser/resources/md_history/history_list.js
diff --git a/chrome/browser/resources/md_history/history_list.js b/chrome/browser/resources/md_history/history_list.js
index a510e6902161bf92dcb9a99d699f341e2b97c849..75c74ec3152bf165d9b061f1185795a3e9d3fbfc 100644
--- a/chrome/browser/resources/md_history/history_list.js
+++ b/chrome/browser/resources/md_history/history_list.js
@@ -28,6 +28,12 @@ Polymer({
       value: true
     },
 
+    // True if it's searching at the backend.
+    searching_: {
+      type: Boolean,
+      value: false
+    },
+
     resultLoadingDisabled_: {
       type: Boolean,
       value: false
@@ -51,8 +57,8 @@ Polymer({
   /**
    * Mark the page as currently loading new data from the back-end.
    */
-  setLoading: function() {
-    this.loading_ = true;
+  setSearching: function() {

[tsergeant, 2016/04/07 01:07:02]

We need to be careful about changing when loading_ is true, since it also:

* Disables loading more data by scrolling down
* Controls what messages can appear over the page.

If you want to have a separate searching_ boolean, you'll still need to make
sure that loading_ is true.

[lshang, 2016/04/15 03:31:54]

Done.
Thanks for reminding!

+    this.searching_ = true;
   },
 
   /**
@@ -82,6 +88,7 @@ Polymer({
    */
   addNewResults: function(historyResults, searchTerm) {
     this.loading_ = false;
+    this.searching_ = false;
 
     if (this.searchTerm != searchTerm) {
       if (this.historyData)