Add build option to third_party/http2. No functional change.

I fixed build complains under http2/. However, adding the build rule in BUILD will require change files we don't own. This build failure is an example when adding build rule to BUILD: http://sponge2/26d093f0-c749-4709-b47d-4ba0646407a1.

PiperOrigin-RevId: 324931975
Change-Id: I9296361aaf97cbf36322a52cc017f33185859aa4
diff --git a/http2/hpack/http2_hpack_constants_test.cc b/http2/hpack/http2_hpack_constants_test.cc
index b266554..d44072b 100644
--- a/http2/hpack/http2_hpack_constants_test.cc
+++ b/http2/hpack/http2_hpack_constants_test.cc
@@ -6,9 +6,8 @@
 
 #include <sstream>
 
-#include "testing/gmock/include/gmock/gmock.h"
-#include "testing/gtest/include/gtest/gtest.h"
 #include "net/third_party/quiche/src/http2/platform/api/http2_logging.h"
+#include "net/third_party/quiche/src/http2/platform/api/http2_test_helpers.h"
 
 namespace http2 {
 namespace test {