Avoid collecting symbol info for one-off preparsing.

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 56412a05a54e53f13a834f938c4999dfdad3e65c..c3e947fad92d7c7468b52c2fe5c7d026a7c1a114 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -212,11 +212,17 @@ FunctionLiteral* MakeAST(bool compile_in_global_context,
                          ScriptDataImpl* pre_data,
                          bool is_json = false);
 
-
+// Generic preparser generating full preparse data.
 ScriptDataImpl* PreParse(Handle<String> source,
                          unibrow::CharacterStream* stream,
                          v8::Extension* extension);
 
+// Preparser that only does preprocessing that makes sense if only used
+// immediately after.
+ScriptDataImpl* PartialPreParse(Handle<String> source,
+                                unibrow::CharacterStream* stream,
+                                v8::Extension* extension);
+
 
 bool ParseRegExp(FlatStringReader* input,
                  bool multiline,