Strict mode parameter validation.

src/scanner-base.h

Index: src/scanner-base.h
diff --git a/src/scanner-base.h b/src/scanner-base.h
index 1024ad18582e3c078793d2295fe3cb8a92d23b18..02b747c5b8ed71f8432a4ce0f24319da4567ad03 100644
--- a/src/scanner-base.h
+++ b/src/scanner-base.h
@@ -271,10 +271,19 @@ class Scanner {
   struct Location {
     Location(int b, int e) : beg_pos(b), end_pos(e) { }
     Location() : beg_pos(0), end_pos(0) { }
+
+    bool IsValid() const {
+      return beg_pos >= 0 && end_pos >= beg_pos;
+    }
+
     int beg_pos;
     int end_pos;
   };
 
+  static Location NoLocation() {
+    return Location(-1, -1);
+  }
+
   // Returns the location information for the current token
   // (the token returned by Next()).
   Location location() const { return current_.location; }