[es6] implement default parameters via desugaring

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 49 matching lines @@
 
   // The source code for an eval() call may refer to a variable that is
   // in an outer scope about which we don't know anything (it may not
   // be the script scope). scope() is NULL in that case. Currently the
   // scope is only used to follow the context chain length.
   Scope* scope() const { return scope_; }
 
   Handle<String> name() const { return name_->string(); }
   const AstRawString* raw_name() const { return name_; }
   VariableMode mode() const { return mode_; }
+  void set_mode(VariableMode mode) {
+    // Don't use this unless you have a very good reason
+    mode_ = mode;
+  }
   bool has_forced_context_allocation() const {
     return force_context_allocation_;
   }
   void ForceContextAllocation() {
     DCHECK(mode_ != TEMPORARY);
     force_context_allocation_ = true;
   }
   bool is_used() { return is_used_; }
   void set_is_used() { is_used_ = true; }
   MaybeAssignedFlag maybe_assigned() const { return maybe_assigned_; }
@@ skipping 121 matching lines @@
 
  private:
   // For classes we keep track of consecutive groups of delcarations. They are
   // needed for strong mode scoping checks. TODO(marja, rossberg): Implement
   // checks for functions too.
   int declaration_group_start_;
 };
 } }  // namespace v8::internal
 
 #endif  // V8_VARIABLES_H_