[MD History] Make forward/backward work in grouped mode.

chrome/test/data/webui/md_history/history_toolbar_test.js

Index: chrome/test/data/webui/md_history/history_toolbar_test.js
diff --git a/chrome/test/data/webui/md_history/history_toolbar_test.js b/chrome/test/data/webui/md_history/history_toolbar_test.js
index 6910024eb12f97f2d3aa1bdf5c0304b42d455408..e7d7d16a0ae136f490f9633c77f382ac325f3510 100644
--- a/chrome/test/data/webui/md_history/history_toolbar_test.js
+++ b/chrome/test/data/webui/md_history/history_toolbar_test.js
@@ -93,9 +93,39 @@ cr.define('md_history.history_toolbar_test', function() {
         toolbar.$$('cr-toolbar').fire('search-changed', 'Test2');
       });
 
+      test('grouped history navigation buttons', function() {
+        var info = createHistoryInfo();
+        info.finished = false;
+        app.historyResult(info, []);
+        app.grouped_ = true;
+        return PolymerTest.flushTasks().then(function() {
+          app.set('queryState_.range', HistoryRange.MONTH);
+          groupedList = app.$.history.$$('#grouped-list');
+          assertTrue(!!groupedList);
+          var today = toolbar.$$('#today-button');
+          var next = toolbar.$$('#next-button');
+          var prev = toolbar.$$('#prev-button');
+
+          assertEquals(0, toolbar.groupedOffset);
+          assertTrue(today.disabled);
+          assertTrue(next.disabled);
+          assertFalse(prev.disabled);
+
+          MockInteractions.tap(prev);
+          assertEquals(1, toolbar.groupedOffset);
+          assertFalse(today.disabled);
+          assertFalse(next.disabled);
+          assertFalse(prev.disabled);
+
+          app.historyResult(createHistoryInfo(), []);
+          assertFalse(today.disabled);
+          assertFalse(next.disabled);
+          assertTrue(prev.disabled);
+        });
+      });
+
       teardown(function() {
         registerMessageCallback('queryHistory', this, function() {});
-        app.set('queryState_.searchTerm', '');
       });
     });
   }