Introduce FeedbackVectorSlot type - better than int.

src/compiler/js-generic-lowering.cc

Index: src/compiler/js-generic-lowering.cc
diff --git a/src/compiler/js-generic-lowering.cc b/src/compiler/js-generic-lowering.cc
index d1951e07bb56f8e22f1651d79f4c4fd3b8e1fd8b..7f49fafcbb62812bfe2ef0076a402df9e4b1d3ec 100644
--- a/src/compiler/js-generic-lowering.cc
+++ b/src/compiler/js-generic-lowering.cc
@@ -275,7 +275,8 @@ void JSGenericLowering::LowerJSLoadProperty(Node* node) {
   const LoadPropertyParameters& p = LoadPropertyParametersOf(node->op());
   Callable callable = CodeFactory::KeyedLoadICInOptimizedCode(isolate());
   if (FLAG_vector_ics) {
-    PatchInsertInput(node, 2, jsgraph()->SmiConstant(p.feedback().slot()));
+    PatchInsertInput(node, 2,
+                     jsgraph()->SmiConstant(p.feedback().slot().ToInt()));
     PatchInsertInput(node, 3, jsgraph()->HeapConstant(p.feedback().vector()));
   }
   ReplaceWithStubCall(node, callable, CallDescriptor::kPatchableCallSite);
@@ -288,7 +289,8 @@ void JSGenericLowering::LowerJSLoadNamed(Node* node) {
       CodeFactory::LoadICInOptimizedCode(isolate(), p.contextual_mode());
   PatchInsertInput(node, 1, jsgraph()->HeapConstant(p.name()));
   if (FLAG_vector_ics) {
-    PatchInsertInput(node, 2, jsgraph()->SmiConstant(p.feedback().slot()));
+    PatchInsertInput(node, 2,
+                     jsgraph()->SmiConstant(p.feedback().slot().ToInt()));
     PatchInsertInput(node, 3, jsgraph()->HeapConstant(p.feedback().vector()));
   }
   ReplaceWithStubCall(node, callable, CallDescriptor::kPatchableCallSite);