Bring back setting visible viewport size based on cliprect.

cc/trees/layer_tree_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/animation/keyframed_animation_curve.h"
 #include "cc/animation/scrollbar_animation_controller.h"
 #include "cc/debug/traced_value.h"
@@ skipping 197 matching lines @@
 }
 
 void LayerTreeImpl::UpdateMaxScrollOffset() {
   LayerImpl* root_scroll = RootScrollLayer();
   if (!root_scroll || !root_scroll->children().size())
     return;
 
   gfx::Vector2dF max_scroll = gfx::Rect(ScrollableSize()).bottom_right() -
       gfx::RectF(ScrollableViewportSize()).bottom_right();
 
-  // The scrollable viewport size is based on device viewport instead of Blink's
-  // container layer, so we need to adjust for non-overlay scrollbars.
-  ScrollbarLayerImpl* horiz = root_scroll->horizontal_scrollbar_layer();
-  ScrollbarLayerImpl* vertical = root_scroll->vertical_scrollbar_layer();
-  if (horiz && !horiz->is_overlay_scrollbar())
-    max_scroll.set_y(max_scroll.y() + horiz->thumb_thickness());
-  if (vertical && !vertical->is_overlay_scrollbar())
-    max_scroll.set_x(max_scroll.x() + vertical->thumb_thickness());
-
   // The viewport may be larger than the contents in some cases, such as
   // having a vertical scrollbar but no horizontal overflow.
   max_scroll.SetToMax(gfx::Vector2dF());
 
   root_scroll_layer_->SetMaxScrollOffset(gfx::ToFlooredVector2d(max_scroll));
 }
 
 static void ApplySentScrollDeltasOn(LayerImpl* layer) {
   layer->ApplySentScrollDeltas();
 }
@@ skipping 371 matching lines @@
 const std::vector<LayerImpl*> LayerTreeImpl::LayersWithCopyOutputRequest()
     const {
   // Only the active tree needs to know about layers with copy requests, as
   // they are aborted if not serviced during draw.
   DCHECK(IsActiveTree());
 
   return layers_with_copy_output_request_;
 }
 
 }  // namespace cc