[es6] re-implement rest parameters via desugaring

src/scopes.h

Index: src/scopes.h
diff --git a/src/scopes.h b/src/scopes.h
index 9f913450abd9f7f8622ef1b85082bd4c3e43a15b..67cfe0cabe54ee841eb77892116d7acde6db0488 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -489,6 +489,11 @@ class Scope: public ZoneObject {
   // where var declarations will be hoisted to in the implementation.
   Scope* DeclarationScope();
 
+  // Find the first non-block declaration scope. This should be either a global,
+  // eval or function top scope. Same as DeclarationScope(), but skips
+  // declaration "block" scopes. Used for declaring temporaries.
+  Scope* TempScope();
+
   Handle<ScopeInfo> GetScopeInfo(Isolate* isolate);
 
   // Get the chain of nested scopes within this scope for the source statement