Refactor Parser to make it usable on a background thread.

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index b5bcf529a8caa0bbce36ebf9d2dceaa0ce2fdf0d..fcd230ca8ced86789e39f64cbd6354b3ddb9f505 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -78,8 +78,8 @@ class ParserBase : public Traits {
         fni_(NULL),
         log_(log),
         mode_(PARSE_EAGERLY),  // Lazy mode must be set explicitly.
-        scanner_(scanner),
         stack_limit_(stack_limit),
+        scanner_(scanner),
         stack_overflow_(false),
         allow_lazy_(false),
         allow_natives_syntax_(false),
@@ -569,10 +569,10 @@ class ParserBase : public Traits {
   FuncNameInferrer* fni_;
   ParserRecorder* log_;
   Mode mode_;
+  uintptr_t stack_limit_;
 
  private:
   Scanner* scanner_;
-  uintptr_t stack_limit_;
   bool stack_overflow_;
 
   bool allow_lazy_;