It turns out I had the sense of the GetLocalBounds bool wrong everywhere, so ...

views/controls/scrollbar/native_scroll_bar_gtk.cc

 // Copyright (c) 2009 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 "views/controls/scrollbar/native_scroll_bar_gtk.h"
 
 #include <gtk/gtk.h>
 
 #include "ui/base/keycodes/keyboard_codes_posix.h"
 #include "views/controls/scrollbar/native_scroll_bar.h"
@@ skipping 10 matching lines @@
   set_focus_view(scroll_bar);
 }
 
 NativeScrollBarGtk::~NativeScrollBarGtk() {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // NativeScrollBarGtk, View overrides:
 
 void NativeScrollBarGtk::Layout() {
-  SetBoundsRect(native_scroll_bar_->GetContentsBounds());
+  SetBoundsRect(native_scroll_bar_->GetLocalBounds());
   NativeControlGtk::Layout();
 }
 
 gfx::Size NativeScrollBarGtk::GetPreferredSize() {
   if (native_scroll_bar_->IsHorizontal())
     return gfx::Size(0, GetHorizontalScrollBarHeight());
   return gfx::Size(GetVerticalScrollBarWidth(), 0);
 }
 
 // TODO(oshima|jcampan): key/mouse events are not delievered and
@@ skipping 166 matching lines @@
   return 20;
 }
 
 // static
 int NativeScrollBarWrapper::GetVerticalScrollBarWidth() {
   // TODO(oshima): get this from gtk's widget property "slider-width".
   return 20;
 }
 
 }  // namespace views