Do not look for the slot in the ScopeInfo's global range when it's not necessary.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index dd43f0fe5b08df6f813d7fabd23ed9880c8d1a33..113ba3a67102e687a1b9597c1bafdfa99e96592c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3898,16 +3898,25 @@ class ScopeInfo : public FixedArray {
   // string.
   int StackSlotIndex(String* name);
 
-  // Lookup support for serialized scope info. Returns the
-  // context slot index for a given slot name if the slot is present; otherwise
+  // Lookup support for serialized scope info. Returns the local context slot
+  // index for a given slot name if the slot is present; otherwise
   // returns a value < 0. The name must be an internalized string.
   // If the slot is present and mode != NULL, sets *mode to the corresponding
   // mode for that variable.
   static int ContextSlotIndex(Handle<ScopeInfo> scope_info, Handle<String> name,
-                              VariableMode* mode, VariableLocation* location,
-                              InitializationFlag* init_flag,
+                              VariableMode* mode, InitializationFlag* init_flag,
                               MaybeAssignedFlag* maybe_assigned_flag);
 
+  // Similar to ContextSlotIndex() but this method searches only among
+  // global slots of the serialized scope info. Returns the context slot index
+  // for a given slot name if the slot is present; otherwise returns a
+  // value < 0. The name must be an internalized string. If the slot is present
+  // and mode != NULL, sets *mode to the corresponding mode for that variable.
+  static int ContextGlobalSlotIndex(Handle<ScopeInfo> scope_info,
+                                    Handle<String> name, VariableMode* mode,
+                                    InitializationFlag* init_flag,
+                                    MaybeAssignedFlag* maybe_assigned_flag);
+
   // Lookup the name of a certain context slot by its index.
   String* ContextSlotName(int slot_index);