[es6] Fix scoping for default parameters in arrow functions

src/pattern-rewriter.cc

 // 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/ast.h"
 #include "src/messages.h"
+#include "src/parameter-initializer-rewriter.h"
 #include "src/parser.h"
 
 namespace v8 {
 
 namespace internal {
 
 
 void Parser::PatternRewriter::DeclareAndInitializeVariables(
     Block* block, const DeclarationDescriptor* declaration_descriptor,
     const DeclarationParsingResult::Declaration* declaration,
@@ skipping 335 matching lines @@
   // let {<pattern> = <init>} = <value>
   //   becomes
   // temp = <value>;
   // <pattern> = temp === undefined ? <init> : temp;
   DCHECK(node->op() == Token::ASSIGN);
   auto temp = CreateTempVar(current_value_);
   Expression* is_undefined = factory()->NewCompareOperation(
       Token::EQ_STRICT, factory()->NewVariableProxy(temp),
       factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
       RelocInfo::kNoPosition);
+  Expression* initializer = node->value();
+  if (descriptor_->declaration_kind == DeclarationDescriptor::PARAMETER &&
+      descriptor_->scope->is_arrow_scope()) {
+    // TODO(adamk): Only call this if necessary.
+    RewriteParameterInitializerScope(
+        descriptor_->parser->stack_limit(), initializer,
+        descriptor_->scope->outer_scope(), descriptor_->scope);
+  }
   Expression* value = factory()->NewConditional(
-      is_undefined, node->value(), factory()->NewVariableProxy(temp),
+      is_undefined, initializer, factory()->NewVariableProxy(temp),
       RelocInfo::kNoPosition);
   RecurseIntoSubpattern(node->target(), value);
 }
 
 
 // =============== UNREACHABLE =============================
 
 void Parser::PatternRewriter::Visit(AstNode* node) { UNREACHABLE(); }
 
 #define NOT_A_PATTERN(Node)                                        \
@@ skipping 42 matching lines @@
 NOT_A_PATTERN(TryFinallyStatement)
 NOT_A_PATTERN(UnaryOperation)
 NOT_A_PATTERN(VariableDeclaration)
 NOT_A_PATTERN(WhileStatement)
 NOT_A_PATTERN(WithStatement)
 NOT_A_PATTERN(Yield)
 
 #undef NOT_A_PATTERN
 }  // namespace internal
 }  // namespace v8