Separate JSON parsing from the JavaScript parser.

src/scanner.h

Index: src/scanner.h
diff --git a/src/scanner.h b/src/scanner.h
index 6e5333bce1e5defe347d3f4cac9e3fa51be4e382..dab3d672815fb29803588bdf778226b2201797a3 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -296,6 +296,9 @@ class Scanner {
   // Returns the next token.
   Token::Value Next();
 
+  // Returns the current token again.
+  Token::Value current_token() { return current_.token; }
+
   // One token look-ahead (past the token returned by Next()).
   Token::Value peek() const { return next_.token; }