[es6] implement default parameters via desugaring

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 58253e1bb6919309a444864f10bfff904efb837f..0a46eb3e2d726b1cbc2c999637c6fde9c207c658 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -746,9 +746,10 @@ class ParserTraits {
                             FunctionKind kind = kNormalFunction);
 
   bool DeclareFormalParameter(Scope* scope, const AstRawString* name,
-                              bool is_rest) {
+                              bool is_rest, int pos) {
     bool is_duplicate = false;
-    Variable* var = scope->DeclareParameter(name, VAR, is_rest, &is_duplicate);
+    Variable* var =
+        scope->DeclareParameter(name, VAR, pos, is_rest, &is_duplicate);

[arv (Not doing code reviews), 2015/05/06 20:32:38]

keep pos at end?

     if (is_sloppy(scope->language_mode())) {
       // TODO(sigurds) Mark every parameter as maybe assigned. This is a
       // conservative approximation necessary to account for parameters
@@ -978,6 +979,9 @@ class Parser : public ParserBase<ParserTraits> {
       ForStatement* loop, Statement* init, Expression* cond, Statement* next,
       Statement* body, bool* ok);
 
+  ZoneList<Statement*>* DesugarInitializeParameters(
+      Scope* scope, bool has_initializers, ZoneList<Expression*>* initializers);
+
   FunctionLiteral* ParseFunctionLiteral(
       const AstRawString* name, Scanner::Location function_name_location,
       bool name_is_strict_reserved, FunctionKind kind,
@@ -1011,6 +1015,10 @@ class Parser : public ParserBase<ParserTraits> {
   VariableProxy* NewUnresolved(const AstRawString* name, VariableMode mode);
   Variable* Declare(Declaration* declaration, bool resolve, bool* ok);
 
+  // Parameters have expressions --- ensure that the declared parameters can
+  // never be resolved
+  void ShadowParametersForExpressions(Scope* scope);
+
   bool TargetStackContainsLabel(const AstRawString* label);
   BreakableStatement* LookupBreakTarget(const AstRawString* label, bool* ok);
   IterationStatement* LookupContinueTarget(const AstRawString* label, bool* ok);