Move MockVisitor to an anonymous namesapce in qpack_decoded_headers_accumulator_test.cc
to avoid some baffling namespace collision in chromium

gfe-relnote: n/a - Test only
PiperOrigin-RevId: 280518833
Change-Id: I8c09980947b27b25b0addfc7bd49d2c97dc89cd2

quic/core/qpack/qpack_decoded_headers_accumulator_test.cc

diff --git a/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc b/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc
index 11d4289..a4f7f14 100644
--- a/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc
+++ b/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc
@@ -38,8 +38,6 @@
 // Header Acknowledgement decoder stream instruction with stream_id = 1.
 const char* const kHeaderAcknowledgement = "\x81";
 
-}  // anonymous namespace
-
 class MockVisitor : public QpackDecodedHeadersAccumulator::Visitor {
  public:
   ~MockVisitor() override = default;
@@ -47,6 +45,8 @@
   MOCK_METHOD1(OnHeaderDecodingError, void(QuicStringPiece error_message));
 };
 
+}  // anonymous namespace
+
 class QpackDecodedHeadersAccumulatorTest : public QuicTest {
  protected:
   QpackDecodedHeadersAccumulatorTest()