DevTools: expose setLayerTreeId() so we can relate events from LayerTreeHost

Source/core/inspector/InspectorInstrumentation.cpp

Index: Source/core/inspector/InspectorInstrumentation.cpp
diff --git a/Source/core/inspector/InspectorInstrumentation.cpp b/Source/core/inspector/InspectorInstrumentation.cpp
index fc2937fe30b8055a98755b40bfcf6e8844f785f7..462ba0b56521db5f34ff632d90c49fab6cedbc23 100644
--- a/Source/core/inspector/InspectorInstrumentation.cpp
+++ b/Source/core/inspector/InspectorInstrumentation.cpp
@@ -234,12 +234,14 @@ const char ImageDecodeTask[] = "ImageDecodeTask";
 const char Paint[] = "Paint";
 const char Layer[] = "Layer";
 const char BeginFrame[] = "BeginFrame";
+const char UpdateLayer[] = "UpdateLayer";
 };
 
 namespace InstrumentationEventArguments {
 const char LayerId[] = "layerId";
-const char PageId[] = "pageId";
+const char LayerTreeId[] = "layerTreeId";
 const char NodeId[] = "nodeId";
+const char PageId[] = "pageId";
 };
 
 InstrumentingAgents* instrumentationForPage(Page* page)