Handle nested position:sticky elements correctly (compositor)

third_party/WebKit/public/platform/WebLayer.h

Index: third_party/WebKit/public/platform/WebLayer.h
diff --git a/third_party/WebKit/public/platform/WebLayer.h b/third_party/WebKit/public/platform/WebLayer.h
index 457ee2ee5a2daa15154c6e180bbfe7234a9f72d4..806e2bf26d360a88a96a3ef040574f41125a45b5 100644
--- a/third_party/WebKit/public/platform/WebLayer.h
+++ b/third_party/WebKit/public/platform/WebLayer.h
@@ -26,6 +26,8 @@
 #ifndef WebLayer_h
 #define WebLayer_h
 
+#include "cc/layers/layer.h"
+
 #include "WebBlendMode.h"
 #include "WebColor.h"
 #include "WebCommon.h"
@@ -58,6 +60,8 @@ class WebLayer {
  public:
   virtual ~WebLayer() {}
 
+  static constexpr int kInvalidLayerId = cc::Layer::INVALID_ID;
+
   // Returns a positive ID that will be unique across all WebLayers allocated in
   // this process.
   virtual int id() const = 0;