Revert of Use Layer::INVALID_ID instead of 0 for invalid layers in WebScrollbarLayerImpl

cc/blink/web_scrollbar_layer_impl.cc

Index: cc/blink/web_scrollbar_layer_impl.cc
diff --git a/cc/blink/web_scrollbar_layer_impl.cc b/cc/blink/web_scrollbar_layer_impl.cc
index d723efb830540ee7520c14d2aec701673c8b245a..b6a759c51471a71433c6a424f18107ad89a7f368 100644
--- a/cc/blink/web_scrollbar_layer_impl.cc
+++ b/cc/blink/web_scrollbar_layer_impl.cc
@@ -39,7 +39,7 @@
           base::MakeUnique<ScrollbarImpl>(std::move(scrollbar),
                                           painter,
                                           std::move(geometry)),
-          cc::Layer::INVALID_ID))) {}
+          0))) {}
 
 WebScrollbarLayerImpl::WebScrollbarLayerImpl(
     std::unique_ptr<blink::WebScrollbar> scrollbar,
@@ -50,7 +50,7 @@
           base::MakeUnique<ScrollbarImpl>(std::move(scrollbar),
                                           painter,
                                           std::move(geometry)),
-          cc::Layer::INVALID_ID))) {}
+          0))) {}
 
 WebScrollbarLayerImpl::WebScrollbarLayerImpl(
     blink::WebScrollbar::Orientation orientation,
@@ -62,7 +62,7 @@
                                            thumb_thickness,
                                            track_start,
                                            is_left_side_vertical_scrollbar,
-                                           cc::Layer::INVALID_ID))) {}
+                                           0))) {}
 
 WebScrollbarLayerImpl::~WebScrollbarLayerImpl() {
 }