Preparser extracted into separate files that can be compiled to a library.

src/preparser.cc

Index: src/preparser.cc
diff --git a/src/preparser.cc b/src/preparser.cc
index 9061731237e8d168ace9aeaebaf45a91b92df5f2..cc6874b4fccf9702f67c289d188f0717fafe6f11 100644
--- a/src/preparser.cc
+++ b/src/preparser.cc
@@ -65,7 +65,7 @@ void PreParser::ReportUnexpectedToken(i::Token::Value token) {
   // We don't report stack overflows here, to avoid increasing the
   // stack depth even further.  Instead we report it after parsing is
   // over, in ParseProgram.
-  if (token == i::Token::ILLEGAL && scanner_->stack_overflow()) {
+  if (token == i::Token::ILLEGAL && stack_overflow_) {
     return;
   }
   i::JavaScriptScanner::Location source_location = scanner_->location();