Sloppy-mode let parsing

src/scanner.cc

Index: src/scanner.cc
diff --git a/src/scanner.cc b/src/scanner.cc
index c6c0a8d6a23448b7be244224ec48bc5b37b16cee..f6c10b44034e02c5ee3a801fa3f9264ea7049937 100644
--- a/src/scanner.cc
+++ b/src/scanner.cc
@@ -238,6 +238,11 @@ Token::Value Scanner::Next() {
     next_.location.end_pos = current_.location.end_pos;
   }
   current_ = next_;
+  if (next_next_.token != Token::UNINITIALIZED) {
+    next_ = next_next_;
+    next_next_.token = Token::UNINITIALIZED;
+    return current_.token;
+  }
   has_line_terminator_before_next_ = false;
   has_multiline_comment_before_next_ = false;
   if (static_cast<unsigned>(c0_) <= 0x7f) {
@@ -256,6 +261,20 @@ Token::Value Scanner::Next() {
 }
 
 
+Token::Value Scanner::PeekAhead() {
+  if (next_next_.token != Token::UNINITIALIZED) {
+    return next_next_.token;
+  }
+  TokenDesc prev = current_;
+  Next();
+  Token::Value ret = next_.token;
+  next_next_ = next_;
+  next_ = current_;
+  current_ = prev;
+  return ret;
+}
+
+
 // TODO(yangguo): check whether this is actually necessary.
 static inline bool IsLittleEndianByteOrderMark(uc32 c) {
   // The Unicode value U+FFFE is guaranteed never to be assigned as a