Add parsing for class declarations

src/parsing/preparser.cc

Index: src/parsing/preparser.cc
diff --git a/src/parsing/preparser.cc b/src/parsing/preparser.cc
index 51d7f50ec6592d6b6d0c280ec024b92986bed047..fd125e8919a04642a21b5a128cb956bc75a77c1e 100644
--- a/src/parsing/preparser.cc
+++ b/src/parsing/preparser.cc
@@ -1138,6 +1138,12 @@ PreParserExpression PreParser::ParseClassLiteral(
   // TODO(marja): Make PreParser use scope names too.
   // scope_->SetScopeName(name);
 
+  // Parse optional type parameters.
+  if (scope_->typed() && peek() == Token::LT) {  // Braces required here.
+    ParseTypeParameters(CHECK_OK);
+  }
+
+  // Parse optional extends clause.
   bool has_extends = Check(Token::EXTENDS);
   if (has_extends) {
     ExpressionClassifier classifier(this);
@@ -1145,6 +1151,13 @@ PreParserExpression PreParser::ParseClassLiteral(
     ValidateExpression(&classifier, CHECK_OK);
   }
 
+  // Parse optional implements clause.
+  if (scope_->typed() && CheckContextualKeyword(CStrVector("implements"))) {
+    do {
+      ParseTypeReference(CHECK_OK);
+    } while (Check(Token::COMMA));
+  }
+
   ClassLiteralChecker checker(this);
   bool has_seen_constructor = false;