Made layout viewport scroll updates from compositor work like ordinary layers.

cc/trees/tree_synchronizer_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/tree_synchronizer.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <set>
@@ skipping 609 matching lines @@
   // Set ScrollOffset active delta: gfx::ScrollOffset(10, 10)
   LayerImpl* scroll_layer_impl =
       host_impl->active_tree()->LayerById(scroll_layer->id());
   ScrollTree& scroll_tree =
       host_impl->active_tree()->property_trees()->scroll_tree;
   scroll_tree.SetScrollOffset(scroll_layer_impl->id(),
                               gfx::ScrollOffset(20, 30));
 
   // Pull ScrollOffset delta for main thread, and change offset on main thread
   std::unique_ptr<ScrollAndScaleSet> scroll_info(new ScrollAndScaleSet());
-  scroll_tree.CollectScrollDeltas(scroll_info.get());
+  scroll_tree.CollectScrollDeltas(scroll_info.get(), Layer::INVALID_ID);
   host_->proxy()->SetNeedsCommit();
   host_->ApplyScrollAndScale(scroll_info.get());
   EXPECT_EQ(gfx::ScrollOffset(20, 30), scroll_layer->scroll_offset());
   scroll_layer->SetScrollOffset(gfx::ScrollOffset(100, 100));
 
   // More update to ScrollOffset active delta: gfx::ScrollOffset(20, 20)
   scroll_tree.SetScrollOffset(scroll_layer_impl->id(),
                               gfx::ScrollOffset(40, 50));
   host_impl->active_tree()->SetCurrentlyScrollingLayer(scroll_layer_impl);
 
@@ skipping 58 matching lines @@
   host_->CommitAndCreatePendingTree();
   host_impl->ActivateSyncTree();
   EXPECT_EQ(
       CombinedAnimationScale(0.f, 0.f),
       host_impl->active_tree()->property_trees()->GetAnimationScales(
           transform_layer->transform_tree_index(), host_impl->active_tree()));
 }
 
 }  // namespace
 }  // namespace cc