[parser] implement error reporting for Scanner errors

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index 5415eef42c78180c1e73e65d225882b1918ce8af..0eef2d2b39d08c14a42c02fe70612abf34c8cf43 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -1012,6 +1012,10 @@ void ParserBase<Traits>::ReportUnexpectedTokenAt(
     Scanner::Location source_location, Token::Value token,
     MessageTemplate::Template message) {
   const char* arg;
+  if (token == Token::ILLEGAL && scanner()->has_error()) {

[adamk, 2016/03/18 18:21:55]

Can you put this logic inside GetUnexpectedToken instead? That'll require adding
a Scanner::Location* arg, but that seems fine.

[caitp (gmail), 2016/03/21 16:15:03]

Done.

+    Traits::ReportMessageAt(scanner()->error_location(), scanner()->error());
+    return;
+  }
   GetUnexpectedTokenMessage(token, &message, &arg);
   Traits::ReportMessageAt(source_location, message, arg);
 }