[esnext] implement frontend changes for async/await proposal

src/parsing/scanner.h

Index: src/parsing/scanner.h
diff --git a/src/parsing/scanner.h b/src/parsing/scanner.h
index b4c6b62d1488f5654869ca4e9bfedd2c03f79f1f..9a3dd8a02a28039bea1c10a22474cce01ce01315 100644
--- a/src/parsing/scanner.h
+++ b/src/parsing/scanner.h
@@ -371,6 +371,10 @@ class Scanner {
   Token::Value peek() const { return next_.token; }
 
   Location peek_location() const { return next_.location; }
+  Location peek_ahead_location() const {
+    DCHECK(next_next_.token != Token::UNINITIALIZED);
+    return next_next_.location;
+  }
 
   bool literal_contains_escapes() const {
     return LiteralContainsEscapes(current_);
@@ -387,8 +391,14 @@ class Scanner {
     return next_.literal_chars->is_contextual_keyword(keyword);
   }
 
+  bool is_next_next_contextual_keyword(Vector<const char> keyword) {
+    DCHECK_NOT_NULL(next_next_.literal_chars);
+    return next_next_.literal_chars->is_contextual_keyword(keyword);
+  }
+
   const AstRawString* CurrentSymbol(AstValueFactory* ast_value_factory);
   const AstRawString* NextSymbol(AstValueFactory* ast_value_factory);
+  const AstRawString* NextNextSymbol(AstValueFactory* ast_value_factory);
   const AstRawString* CurrentRawSymbol(AstValueFactory* ast_value_factory);
 
   double DoubleValue();
@@ -442,6 +452,13 @@ class Scanner {
            has_multiline_comment_before_next_;
   }
 
+  bool HasAnyLineTerminatorAfterNext() {
+    Token::Value ensure_next_next = PeekAhead();
+    USE(ensure_next_next);
+    return has_line_terminator_before_next2_ ||
+           has_multiline_comment_before_next2_;
+  }
+
   // Scans the input as a regular expression pattern, previous
   // character(s) must be /(=). Returns true if a pattern is scanned.
   bool ScanRegExpPattern(bool seen_equal);
@@ -787,6 +804,10 @@ class Scanner {
   // line-terminator after the current token, and before the next.
   bool has_multiline_comment_before_next_;
 
+  // For use with PeekAhead()
+  bool has_line_terminator_before_next2_;
+  bool has_multiline_comment_before_next2_;
+
   // Whether this scanner encountered an HTML comment.
   bool found_html_comment_;