Guard against division by zero for useless scroll bars.

ui/views/controls/scrollbar/base_scroll_bar.h

 // 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.
 
 #ifndef UI_VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_H_
 #define UI_VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "ui/views/animation/scroll_animator.h"
@@ skipping 97 matching lines @@
   // Wrapper functions that calls the controller. We need this since native
   // scrollbars wrap around a different scrollbar. When calling the controller
   // we need to pass in the appropriate scrollbar. For normal scrollbars it's
   // the |this| scrollbar, for native scrollbars it's the native scrollbar used
   // to create this.
   virtual void ScrollToPosition(int position);
   virtual int GetScrollIncrement(bool is_page, bool is_positive);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(NativeScrollBarTest, ScrollBarFitsToBottom);
+  FRIEND_TEST_ALL_PREFIXES(NativeScrollBarTest, ThumbFullLengthOfTrack);
   int GetThumbSizeForTest();
 
   // Changes to 'pushed' state and starts a timer to scroll repeatedly.
   void ProcessPressEvent(const ui::LocatedEvent& event);
 
   // Sets state to |state| and stops the repeater.
   void SetState(CustomButton::ButtonState state);
 
   // Called when the mouse is pressed down in the track area.
   void TrackClicked();
@@ skipping 56 matching lines @@
   // TODO(tdresser): This should be removed when raw pixel scrolling for views
   // is enabled. See crbug.com/329354.
   gfx::Vector2dF roundoff_error_;
 
   DISALLOW_COPY_AND_ASSIGN(BaseScrollBar);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_H_