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

chrome/browser/resources/md_history/history_list.html

Index: chrome/browser/resources/md_history/history_list.html
diff --git a/chrome/browser/resources/md_history/history_list.html b/chrome/browser/resources/md_history/history_list.html
index 59cb64c8712f1443b86501d3bd51d9807637d0fd..40f5c377d338fc08b7d87581f357a8ccaa04938c 100644
--- a/chrome/browser/resources/md_history/history_list.html
+++ b/chrome/browser/resources/md_history/history_list.html
@@ -1,6 +1,7 @@
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-item.html">
+<link rel="import" href="chrome://resources/polymer/v1_0/paper-spinner/paper-spinner.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_shared_menu/cr_shared_menu.html">
 <link rel="import" href="chrome://history/constants.html">
 <link rel="import" href="chrome://history/history_item.html">
@@ -20,6 +21,15 @@
         padding-top: var(--first-card-padding-top);
       }
 
+      #loading-spinner {
+        bottom: 15px;
+        left: 200px;

[tsergeant, 2016/04/15 05:14:50]

This 200px is good when the sidebar exists, but when the user is signed out and
there is no sidebar, then the spinner will be off-center again.

One way to solve this is to set `position: relative` on the <history-list> (in
the :host block above).

Then, the #loading-spinner gets positioned relative to the <history-list>
instead of relative to the whole page.

[lshang, 2016/04/18 00:29:00]

Done.
An absolute position element is positioned relative to the first parent element
that has a position other than static. OMG CSS is so mysterious!

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

Yup, it's pretty weird sometimes.

+        margin: 0 auto;
+        position: absolute;
+        right: 0;
+        width: 28px;
+      }
+
       paper-item {
         -webkit-user-select: none;
         cursor: pointer;
@@ -48,6 +58,9 @@
         </history-item>
       </template>
     </iron-list>
+    <div id="loading-spinner" hidden$="[[!loading_]]">
+      <paper-spinner alt="Loading more history" active></paper-spinner>

[tsergeant, 2016/04/15 05:14:50]

The "Loading more history" string needs to be localized.

I think it would be fine to reuse the "Loading..." string from history.html,
which can be accessed with `$i18n{loading}`

[lshang, 2016/04/18 00:28:59]

Done.

+    </div>
     <cr-shared-menu id="sharedMenu">
       <paper-item id="menuMoreButton" on-tap="onMoreFromSiteTap_">
         $i18n{moreFromSite}