[es6] Re-implement rest parameters via desugaring.

src/pattern-rewriter.cc

Index: src/pattern-rewriter.cc
diff --git a/src/pattern-rewriter.cc b/src/pattern-rewriter.cc
index f7e5b434664ce5905effdbee891e44859ae77aea..372b1801347712a9812db040b2614bac66d24433 100644
--- a/src/pattern-rewriter.cc
+++ b/src/pattern-rewriter.cc
@@ -212,6 +212,14 @@ void Parser::PatternRewriter::VisitVariableProxy(VariableProxy* pattern) {
 }
 
 
+void Parser::PatternRewriter::VisitRestParameter(RestParameter* node) {
+  // Rest parameter rewriting handled specially in the parser, but must still
+  // be declared.
+  DCHECK_EQ(DeclarationDescriptor::PARAMETER, descriptor_->declaration_kind);
+  VisitVariableProxy(node->parameter());
+}
+
+
 Variable* Parser::PatternRewriter::CreateTempVar(Expression* value) {
   auto temp = descriptor_->parser->scope_->NewTemporary(
       ast_value_factory()->empty_string());