harmony-scoping: make assignment to 'const' a late error.

src/full-codegen.h

Index: src/full-codegen.h
diff --git a/src/full-codegen.h b/src/full-codegen.h
index 73a6c412ee9021cafc56e48af6fe6e0db28654b9..1439942db8ae33785ce817ba91d3c669e34cddf9 100644
--- a/src/full-codegen.h
+++ b/src/full-codegen.h
@@ -586,6 +586,19 @@ class FullCodeGenerator: public AstVisitor {
   // is expected in the accumulator.
   void EmitAssignment(Expression* expr);
 
+  // Shall an error be thrown if assignment with 'op' operation is perfomed
+  // on this variable in given language mode?
+  static bool IsSignallingAssignmentToConst(Variable* var, Token::Value op,
+                                            StrictMode strict_mode) {
+    if (var->mode() == CONST) return op != Token::INIT_CONST;
+
+    if (var->mode() == CONST_LEGACY) {
+      return strict_mode == STRICT && op != Token::INIT_CONST_LEGACY;
+    }
+
+    return false;
+  }
+
   // Complete a variable assignment.  The right-hand-side value is expected
   // in the accumulator.
   void EmitVariableAssignment(Variable* var,