Fade out overlay scrollbar after page load

cc/trees/layer_tree_host_impl_unittest.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_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 2901 matching lines @@
     std::unique_ptr<SolidColorScrollbarLayerImpl> scrollbar =
         SolidColorScrollbarLayerImpl::Create(host_impl_->active_tree(), 400,
                                              VERTICAL, 10, 0, false, true);
     scrollbar->test_properties()->opacity = 0.f;
     EXPECT_FLOAT_EQ(0.f, scrollbar->test_properties()->opacity);
 
     LayerImpl* scroll = host_impl_->active_tree()->OuterViewportScrollLayer();
     LayerImpl* root = host_impl_->active_tree()->InnerViewportContainerLayer();
     scrollbar->SetScrollElementId(scroll->element_id());
     root->test_properties()->AddChild(std::move(scrollbar));
-    scroll->set_needs_show_scrollbars(true);
     host_impl_->active_tree()->BuildPropertyTreesForTesting();
     host_impl_->active_tree()->DidBecomeActive();
     host_impl_->active_tree()->HandleScrollbarShowRequestsFromMain();
     DrawFrame();
 
     // SetScrollElementId will initialize the scrollbar which will cause it to
     // show and request a redraw.
     did_request_redraw_ = false;
   }
 
@@ skipping 283 matching lines @@
                                            VERTICAL, 10, 0, false, true);
   scrollbar->test_properties()->opacity = 0.f;
   LayerImpl* scroll = host_impl_->pending_tree()->OuterViewportScrollLayer();
   LayerImpl* container =
       host_impl_->pending_tree()->InnerViewportContainerLayer();
   scrollbar->SetScrollElementId(scroll->element_id());
   scrollbar->SetBounds(gfx::Size(10, 100));
   scrollbar->SetPosition(gfx::PointF(90, 0));
   container->test_properties()->AddChild(std::move(scrollbar));
   host_impl_->pending_tree()->PushPageScaleFromMainThread(1.f, 1.f, 1.f);
-  scroll->set_needs_show_scrollbars(true);
   host_impl_->pending_tree()->BuildPropertyTreesForTesting();
   host_impl_->ActivateSyncTree();
 
   ScrollbarAnimationController* scrollbar_controller =
       host_impl_->ScrollbarAnimationControllerForElementId(
           scroll->element_id());
 
   // Scrollbars will flash shown but we should have a fade out animation
   // queued. Run it and fade out the scrollbars.
   {
@@ skipping 9128 matching lines @@
     else
       EXPECT_FALSE(tile->HasRasterTask());
   }
   Region expected_invalidation(
       raster_source->GetRectForImage(checkerable_image->uniqueID()));
   EXPECT_EQ(expected_invalidation, *(root->GetPendingInvalidation()));
 }
 
 }  // namespace
 }  // namespace cc