Handle two non-operators as if they were operators to prevent a failure when assertions are enabled

Change-Id: Ia2011d240866ac9f569aa9aacc374e33c89d74d0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127680
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

Author: bwilkerson

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -586,7 +586,9 @@ class AstBuilder extends StackListener {
         optional('.', operatorToken) ||
         optional('?.', operatorToken) ||
         optional('..', operatorToken) ||
-        optional('?..', operatorToken));
+        optional('?..', operatorToken) ||
+        optional('===', operatorToken) ||
+        optional('!==', operatorToken));
     debugEvent("BinaryExpression");
 
     if (identical(".", operatorToken.stringValue) ||