Make sure that names of temporaries do not clash with real variables.

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 0326fc9996b6f8a1ed761e5e11ad614f35b2dbf9..c2fd015491bd0e117b1d0bc86ac87f8601f1be11 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -2842,7 +2842,12 @@ Statement* Parser::ParseForStatement(ZoneStringList* labels, bool* ok) {
 
         // TODO(keuchel): Move the temporary variable to the block scope, after
         // implementing stack allocated block scoped variables.
-        Variable* temp = top_scope_->DeclarationScope()->NewTemporary(name);
+        Factory* heap_factory = isolate()->factory();
+        Handle<String> dot =
+            heap_factory->NewStringFromAscii(CStrVector(".for."));
+        Handle<String> tempstr = heap_factory->NewConsString(dot, name);
+        Handle<String> tempname = heap_factory->LookupSymbol(tempstr);
+        Variable* temp = top_scope_->DeclarationScope()->NewTemporary(tempname);
         VariableProxy* temp_proxy = factory()->NewVariableProxy(temp);
         ForInStatement* loop = factory()->NewForInStatement(labels);
         Target target(&this->target_stack_, loop);