Update local BaseScrollBar::contents_scroll_offset_ on Update.

ui/views/controls/scrollbar/scrollbar_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/controls/scrollbar/native_scroll_bar.h"
 #include "ui/views/controls/scrollbar/native_scroll_bar_views.h"
 #include "ui/views/controls/scrollbar/scroll_bar.h"
 #include "ui/views/test/views_test_base.h"
 #include "ui/views/widget/widget.h"
 
@@ skipping 138 matching lines @@
   EXPECT_EQ(0, scrollbar_->GetPosition());
   EXPECT_EQ(99, scrollbar_->GetMaxPosition());
   EXPECT_EQ(0, scrollbar_->GetMinPosition());
 
   scrollbar_->Update(100, 199, 99);
   EXPECT_EQ(
       scrollbar_->GetTrackBounds().width() - scrollbar_->GetThumbSizeForTest(),
       scrollbar_->GetPosition());
 }
 
+TEST_F(NativeScrollBarTest, ScrollToEndAfterShrinkAndExpand) {
+  // Scroll to the end of the content.
+  scrollbar_->Update(100, 101, 0);
+  EXPECT_TRUE(scrollbar_->ScrollByContentsOffset(-1));
+  // Shrink and then re-exapnd the content.
+  scrollbar_->Update(100, 100, 0);
+  scrollbar_->Update(100, 101, 0);
+  // Ensure the scrollbar allows scrolling to the end.
+  EXPECT_TRUE(scrollbar_->ScrollByContentsOffset(-1));
+}
+
 }  // namespace views