[esnext] implement frontend changes for async/await proposal

src/parsing/scanner.cc

Index: src/parsing/scanner.cc
diff --git a/src/parsing/scanner.cc b/src/parsing/scanner.cc
index faec88b8a4bfb5ff37bf8dad58fefc32cd8ff03f..84635d779171e46890cc8ad267745acf9f457d66 100644
--- a/src/parsing/scanner.cc
+++ b/src/parsing/scanner.cc
@@ -249,6 +249,8 @@ Token::Value Scanner::Next() {
   if (V8_UNLIKELY(next_next_.token != Token::UNINITIALIZED)) {
     next_ = next_next_;
     next_next_.token = Token::UNINITIALIZED;
+    has_line_terminator_before_next_ = has_line_terminator_before_next2_;
+    has_multiline_comment_before_next_ = has_multiline_comment_before_next2_;
     return current_.token;
   }
   has_line_terminator_before_next_ = false;
@@ -274,7 +276,13 @@ Token::Value Scanner::PeekAhead() {
     return next_next_.token;
   }
   TokenDesc prev = current_;
+  bool has_line_terminator_before_next = has_line_terminator_before_next_;
+  bool has_multiline_comment_before_next = has_multiline_comment_before_next_;
   Next();
+  has_line_terminator_before_next2_ = has_line_terminator_before_next_;
+  has_multiline_comment_before_next2_ = has_multiline_comment_before_next_;
+  has_line_terminator_before_next_ = has_line_terminator_before_next;
+  has_multiline_comment_before_next_ = has_multiline_comment_before_next;

[Dan Ehrenberg, 2016/05/05 01:14:40]

From my experience with let, I'd predict that maintaining these will cause a
noticeable regression on CodeLoad. I wonder if we could consolidate them into
one variable. I only see a single usage which separates the two--detecting
-->-style comments inside of SkipWhiteSpace. Do you think there's any way we
might refactor this?

[caitp (gmail), 2016/05/05 01:36:57]

Well, I've done this in the simplest way I could, so it's very likely it could
be done better. Maybe it's worth a look at the CodeLoad impact before that,
though?

[caitp (gmail), 2016/05/05 21:49:36]

I've had a go at refactoring this --- I doubt it has any substantial improvement
on CodeLoad, but maybe.

   Token::Value ret = next_.token;
   next_next_ = next_;
   next_ = current_;
@@ -1469,6 +1477,15 @@ const AstRawString* Scanner::NextSymbol(AstValueFactory* ast_value_factory) {
   return ast_value_factory->GetTwoByteString(next_literal_two_byte_string());
 }
 
+const AstRawString* Scanner::NextNextSymbol(
+    AstValueFactory* ast_value_factory) {
+  DCHECK(next_next_.token != Token::UNINITIALIZED);
+  LiteralBuffer* literal = next_next_.literal_chars;
+  if (literal->is_one_byte()) {
+    return ast_value_factory->GetOneByteString(literal->one_byte_literal());
+  }
+  return ast_value_factory->GetTwoByteString(literal->two_byte_literal());
+}
 
 const AstRawString* Scanner::CurrentRawSymbol(
     AstValueFactory* ast_value_factory) {