[es6] Fix scoping for default parameters in arrow functions

src/parameter-initializer-rewriter.cc

Index: src/parameter-initializer-rewriter.cc
diff --git a/src/parameter-initializer-rewriter.cc b/src/parameter-initializer-rewriter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ea2e34b6b0702fecd7ee64183506260c564da146
--- /dev/null
+++ b/src/parameter-initializer-rewriter.cc
@@ -0,0 +1,66 @@
+// Copyright 2015 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.
+
+#include "src/v8.h"
+
+#include "src/parameter-initializer-rewriter.h"
+
+#include "src/ast.h"
+#include "src/ast-expression-visitor.h"
+#include "src/scopes.h"
+
+namespace v8 {
+namespace internal {
+
+namespace {
+
+
+class Rewriter final : public AstExpressionVisitor {
+ public:
+  Rewriter(uintptr_t stack_limit, Expression* initializer, Scope* old_scope,
+           Scope* new_scope)
+      : AstExpressionVisitor(stack_limit, initializer),
+        old_scope_(old_scope),
+        new_scope_(new_scope) {}
+
+ private:
+  void VisitExpression(Expression* expr) override {}
+
+  void VisitFunctionLiteral(FunctionLiteral* expr) override;
+  void VisitVariableProxy(VariableProxy* expr) override;
+
+  // TODO(adamk): Need to fix up the scope chain of class literals.
+  // void VisitClassLiteral(ClassLiteral* expr) override;
+
+  Scope* old_scope_;
+  Scope* new_scope_;
+};
+
+
+void Rewriter::VisitFunctionLiteral(FunctionLiteral* function_literal) {
+  function_literal->scope()->set_outer_scope(new_scope_);
+}
+
+
+void Rewriter::VisitVariableProxy(VariableProxy* proxy) {
+  CHECK(!proxy->is_resolved());
+  if (old_scope_->RemoveUnresolved(proxy)) {
+    new_scope_->AddUnresolved(proxy);
+  }
+}
+
+
+}  // anonymous namespace
+
+
+void RewriteParameterInitializerScope(uintptr_t stack_limit,
+                                      Expression* initializer, Scope* old_scope,
+                                      Scope* new_scope) {
+  Rewriter rewriter(stack_limit, initializer, old_scope, new_scope);
+  rewriter.Run();
+}
+
+
+}  // namespace internal
+}  // namespace v8