Disable overlay scrollbars in Blink when hidden by the compositor.

cc/input/scrollbar_animation_controller_linear_fade_unittest.cc

 // Copyright 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 "cc/input/scrollbar_animation_controller_linear_fade.h"
 
 #include "cc/layers/solid_color_scrollbar_layer_impl.h"
 #include "cc/test/fake_impl_task_runner_provider.h"
 #include "cc/test/fake_layer_tree_host_impl.h"
 #include "cc/test/geometry_test_utils.h"
@@ skipping 23 matching lines @@
   }
   void SetNeedsRedrawForScrollbarAnimation() override {
     did_request_redraw_ = true;
   }
   void SetNeedsAnimateForScrollbarAnimation() override {
     did_request_animate_ = true;
   }
   ScrollbarSet ScrollbarsFor(int scroll_layer_id) const override {
     return host_impl_.ScrollbarsFor(scroll_layer_id);
   }
+  void SetScrollbarsHidden(int layer_id, bool hidden) override {}
 
  protected:
   void SetUp() override {
     const int kThumbThickness = 10;
     const int kTrackStart = 0;
     const bool kIsLeftSideVerticalScrollbar = false;
     const bool kIsOverlayScrollbar = true;  // Allow opacity animations.
 
     std::unique_ptr<LayerImpl> scroll_layer =
         LayerImpl::Create(host_impl_.active_tree(), 1);
@@ skipping 444 matching lines @@
   EXPECT_FLOAT_EQ(1, scrollbar_layer_->Opacity());
 
   time += base::TimeDelta::FromSeconds(1);
   scrollbar_controller_->DidScrollEnd();
   EXPECT_FALSE(did_request_animate_);
   EXPECT_FLOAT_EQ(1, scrollbar_layer_->Opacity());
 }
 
 }  // namespace
 }  // namespace cc