Replace layer id with Element id for tracking scrollbar animation controllers

cc/trees/layer_tree_host_pixeltest_scrollbars.cc

Index: cc/trees/layer_tree_host_pixeltest_scrollbars.cc
diff --git a/cc/trees/layer_tree_host_pixeltest_scrollbars.cc b/cc/trees/layer_tree_host_pixeltest_scrollbars.cc
index 9e6c405beb30975c4df108bc26cc27d51d3ac032..eb2fe9558656c52eecfb4b39ae7de3a7f87477d7 100644
--- a/cc/trees/layer_tree_host_pixeltest_scrollbars.cc
+++ b/cc/trees/layer_tree_host_pixeltest_scrollbars.cc
@@ -87,8 +87,8 @@ TEST_F(LayerTreeHostScrollbarsPixelTest, NoScale) {
       CreateSolidColorLayer(gfx::Rect(200, 200), SK_ColorWHITE);
 
   auto scrollbar = base::MakeUnique<PaintedScrollbar>();
-  scoped_refptr<PaintedScrollbarLayer> layer =
-      PaintedScrollbarLayer::Create(std::move(scrollbar), Layer::INVALID_ID);
+  scoped_refptr<PaintedScrollbarLayer> layer = PaintedScrollbarLayer::Create(
+      std::move(scrollbar), Layer::INVALID_ID, ElementId());
   layer->SetIsDrawable(true);
   layer->SetBounds(gfx::Size(200, 200));
   background->AddChild(layer);
@@ -106,8 +106,8 @@ TEST_F(LayerTreeHostScrollbarsPixelTest, DeviceScaleFactor) {
       CreateSolidColorLayer(gfx::Rect(100, 100), SK_ColorWHITE);
 
   auto scrollbar = base::MakeUnique<PaintedScrollbar>();
-  scoped_refptr<PaintedScrollbarLayer> layer =
-      PaintedScrollbarLayer::Create(std::move(scrollbar), Layer::INVALID_ID);
+  scoped_refptr<PaintedScrollbarLayer> layer = PaintedScrollbarLayer::Create(
+      std::move(scrollbar), Layer::INVALID_ID, ElementId());
   layer->SetIsDrawable(true);
   layer->SetBounds(gfx::Size(100, 100));
   background->AddChild(layer);
@@ -121,8 +121,8 @@ TEST_F(LayerTreeHostScrollbarsPixelTest, TransformScale) {
       CreateSolidColorLayer(gfx::Rect(200, 200), SK_ColorWHITE);
 
   auto scrollbar = base::MakeUnique<PaintedScrollbar>();
-  scoped_refptr<PaintedScrollbarLayer> layer =
-      PaintedScrollbarLayer::Create(std::move(scrollbar), Layer::INVALID_ID);
+  scoped_refptr<PaintedScrollbarLayer> layer = PaintedScrollbarLayer::Create(
+      std::move(scrollbar), Layer::INVALID_ID, ElementId());
   layer->SetIsDrawable(true);
   layer->SetBounds(gfx::Size(100, 100));
   background->AddChild(layer);
@@ -143,8 +143,8 @@ TEST_F(LayerTreeHostScrollbarsPixelTest, HugeTransformScale) {
 
   auto scrollbar = base::MakeUnique<PaintedScrollbar>();
   scrollbar->set_paint_scale(1);
-  scoped_refptr<PaintedScrollbarLayer> layer =
-      PaintedScrollbarLayer::Create(std::move(scrollbar), Layer::INVALID_ID);
+  scoped_refptr<PaintedScrollbarLayer> layer = PaintedScrollbarLayer::Create(
+      std::move(scrollbar), Layer::INVALID_ID, ElementId());
   layer->SetIsDrawable(true);
   layer->SetBounds(gfx::Size(10, 400));
   background->AddChild(layer);
@@ -240,7 +240,7 @@ TEST_F(LayerTreeHostOverlayScrollbarsPixelTest, NinePatchScrollbarScaledUp) {
   auto scrollbar = base::MakeUnique<PaintedOverlayScrollbar>();
   scoped_refptr<PaintedOverlayScrollbarLayer> layer =
       PaintedOverlayScrollbarLayer::Create(std::move(scrollbar),
-                                           Layer::INVALID_ID);
+                                           Layer::INVALID_ID, ElementId());
 
   scrollbar_layer_id_ = layer->id();
   thickness_scale_ = 5.f;
@@ -265,7 +265,7 @@ TEST_F(LayerTreeHostOverlayScrollbarsPixelTest, NinePatchScrollbarScaledDown) {
   auto scrollbar = base::MakeUnique<PaintedOverlayScrollbar>();
   scoped_refptr<PaintedOverlayScrollbarLayer> layer =
       PaintedOverlayScrollbarLayer::Create(std::move(scrollbar),
-                                           Layer::INVALID_ID);
+                                           Layer::INVALID_ID, ElementId());
 
   scrollbar_layer_id_ = layer->id();
   thickness_scale_ = 0.4f;