Track the currently scrolling ScrollNode instead of the scrolling layer

cc/trees/layer_tree_host_unittest_scroll.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/trees/layer_tree_host.h"
 
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 680 matching lines @@
       case 0: {
         // GESTURE scroll on impl thread. Also tests that the last scrolled
         // layer id is stored even after the scrolling ends.
         gfx::Point scroll_point =
             gfx::ToCeiledPoint(expected_scroll_layer_impl->position() -
                                gfx::Vector2dF(0.5f, 0.5f));
         InputHandler::ScrollStatus status = impl->ScrollBegin(
             BeginState(scroll_point).get(), InputHandler::TOUCHSCREEN);
         EXPECT_EQ(InputHandler::SCROLL_ON_IMPL_THREAD, status.thread);
         impl->ScrollBy(UpdateState(gfx::Point(), scroll_amount_).get());
-        LayerImpl* scrolling_layer = impl->CurrentlyScrollingLayer();
-        CHECK(scrolling_layer);
+        auto* scrolling_node = impl->CurrentlyScrollingNode();
+        CHECK(scrolling_node);
         impl->ScrollEnd(EndState().get());
-        CHECK(!impl->CurrentlyScrollingLayer());
-        EXPECT_EQ(scrolling_layer->id(),
-                  impl->active_tree()->LastScrolledLayerId());
+        CHECK(!impl->CurrentlyScrollingNode());
+        EXPECT_EQ(scrolling_node->id,
+                  impl->active_tree()->LastScrolledScrollNodeIndex());
 
         // Check the scroll is applied as a delta.
         EXPECT_VECTOR_EQ(initial_offset_,
                          ScrollTreeForLayer(expected_scroll_layer_impl)
                              ->GetScrollOffsetBaseForTesting(
                                  expected_scroll_layer_impl->id()));
         EXPECT_VECTOR_EQ(scroll_amount_,
                          ScrollDelta(expected_scroll_layer_impl));
         break;
       }
@@ skipping 1519 matching lines @@
   CompletionEvent* impl_side_invalidation_event_ = nullptr;
 
   // Main thread.
   int num_of_deltas_ = 0;
 };
 
 MULTI_THREAD_TEST_F(LayerTreeHostScrollTestImplSideInvalidation);
 
 }  // namespace
 }  // namespace cc