Group lexical context variables for faster look up.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 257f0e54c35d198f2c6ee16d605e961702edf4f7..19ca422bf7ce8b5e472d0669d0c2906996a7cc8e 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3941,6 +3941,9 @@ class ScopeInfo : public FixedArray {
                               InitializationFlag* init_flag,
                               MaybeAssignedFlag* maybe_assigned_flag);
 
+  static int LexicalContextSlotIndex(Handle<ScopeInfo> scope_info,
+                                     Handle<String> name);
+
   // Lookup the name of a certain context slot by its index.
   String* ContextSlotName(int slot_index);
 
@@ -3985,6 +3988,7 @@ class ScopeInfo : public FixedArray {
   V(ParameterCount)               \
   V(StackLocalCount)              \
   V(ContextLocalCount)            \
+  V(LexicalContextLocalCount)     \
   V(ContextGlobalCount)           \
   V(StrongModeFreeVariableCount)