Move Http2Optional to QuicheOptional.

This is part of the overall effort to merge quic, spdy, and http2 platform in
QUICHE.

gfe-relnote: n/a, no functional change.
PiperOrigin-RevId: 289853288
Change-Id: I98711f5dd54db265c29f337a73ad71c5400b227c
diff --git a/http2/test_tools/frame_parts.cc b/http2/test_tools/frame_parts.cc
index 32d3a97..7d5c218 100644
--- a/http2/test_tools/frame_parts.cc
+++ b/http2/test_tools/frame_parts.cc
@@ -507,9 +507,10 @@
   return AssertionSuccess();
 }
 
-AssertionResult FrameParts::AppendString(quiche::QuicheStringPiece source,
-                                         std::string* target,
-                                         Http2Optional<size_t>* opt_length) {
+AssertionResult FrameParts::AppendString(
+    quiche::QuicheStringPiece source,
+    std::string* target,
+    quiche::QuicheOptional<size_t>* opt_length) {
   target->append(source.data(), source.size());
   if (opt_length != nullptr) {
     VERIFY_TRUE(*opt_length) << "Length is not set yet\n" << *this;