Experimental scanner: initialize starting position in literal descriptor.

src/lexer/experimental-scanner.h

Index: src/lexer/experimental-scanner.h
diff --git a/src/lexer/experimental-scanner.h b/src/lexer/experimental-scanner.h
index 7f81565e652db36b77f22747d093b1c36ab9a7b5..ab07ef62e5bda4f91e33e2225421777452ce0912 100644
--- a/src/lexer/experimental-scanner.h
+++ b/src/lexer/experimental-scanner.h
@@ -252,6 +252,7 @@ class ScannerBase {
     Vector<const char> ascii_string;
     Vector<const uc16> utf16_string;
     LiteralBuffer buffer;
+    LiteralDesc() : beg_pos(-1), is_ascii(false), length(0) { }
     bool Valid(int pos) { return beg_pos == pos; }
   };