Strawman: check strong mode free variables against the global object.

src/variables.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_VARIABLES_H_
 #define V8_VARIABLES_H_
 
 #include "src/ast-value-factory.h"
 #include "src/zone.h"
 
@@ skipping 112 matching lines @@
     return initialization_flag_;
   }
 
   void AllocateTo(Location location, int index) {
     location_ = location;
     index_ = index;
   }
 
   static int CompareIndex(Variable* const* v, Variable* const* w);
 
+  void RecordStrongModeReference(int start_position, int end_position) {
+    // Record the earliest reference to the variable. Used in error messages for
+    // strong mode references to undeclared variables.
+    if (has_strong_mode_reference_ &&
+        strong_mode_reference_start_position_ < start_position)
+      return;
+    has_strong_mode_reference_ = true;
+    strong_mode_reference_start_position_ = start_position;
+    strong_mode_reference_end_position_ = end_position;
+  }
+
+  bool has_strong_mode_reference() const { return has_strong_mode_reference_; }
+  int strong_mode_reference_start_position() const {
+    return strong_mode_reference_start_position_;
+  }
+  int strong_mode_reference_end_position() const {
+    return strong_mode_reference_end_position_;
+  }
+
  private:
   Scope* scope_;
   const AstRawString* name_;
   VariableMode mode_;
   Kind kind_;
   Location location_;
   int index_;
   int initializer_position_;
+  // Tracks whether the variable is bound to a VariableProxy which is in strong
+  // mode, and if yes, the source location of the reference.
+  bool has_strong_mode_reference_;
+  int strong_mode_reference_start_position_;
+  int strong_mode_reference_end_position_;
 
   // If this field is set, this variable references the stored locally bound
   // variable, but it might be shadowed by variable bindings introduced by
   // sloppy 'eval' calls between the reference scope (inclusive) and the
   // binding scope (exclusive).
   Variable* local_if_not_shadowed_;
 
   // Valid as a reference? (const and this are not valid, for example)
   bool is_valid_ref_;
 
   // Usage info.
   bool force_context_allocation_;  // set by variable resolver
   bool is_used_;
   InitializationFlag initialization_flag_;
   MaybeAssignedFlag maybe_assigned_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_VARIABLES_H_