Formatter: Handle the case where you have a whole line of forward slashes.

mojom/mojom_parser/formatter/printer.go

Index: mojom/mojom_parser/formatter/printer.go
diff --git a/mojom/mojom_parser/formatter/printer.go b/mojom/mojom_parser/formatter/printer.go
index db79f4e42be7d3fa5826874e06739cb187e24788..adcca5353eafb705c30ed3e0141a0020aab693a5 100644
--- a/mojom/mojom_parser/formatter/printer.go
+++ b/mojom/mojom_parser/formatter/printer.go
@@ -668,7 +668,8 @@ func (p *printer) writeSingleLineComment(comment lexer.Token) {
 
 	// We expect that the first 2 characters are // followed by a space or tab.
 	// If the third character is not a space or tab, we insert a space.
-	if len(commentText) > 2 && commentText[2] != ' ' && commentText[2] != '\t' {
+	// There is an exception for three forward slashes which are allowed.
+	if len(commentText) > 2 && !strings.ContainsAny(" \t/", commentText[2:3]) {
 		commentText = "// " + commentText[2:]
 	}
 	p.write(commentText)