Use testing::Eq() for QuicStringPiece.

A QuicStringPiece argument cannot be verified against a std::string expected
value with Chromium's gMock implementation.  Eq() needs to be used instead.

This is blocking QUICHE merge.  I locally verified that this patch fixed
Chromium compilation.

gfe-relnote: n/a, test-only change.
PiperOrigin-RevId: 258566803
Change-Id: I887a884ea859fc4716fae511984424a158afc22f

quic/core/http/http_decoder_test.cc

diff --git a/quic/core/http/http_decoder_test.cc b/quic/core/http/http_decoder_test.cc
index fbc167c..1c245d0 100644
--- a/quic/core/http/http_decoder_test.cc
+++ b/quic/core/http/http_decoder_test.cc
@@ -12,6 +12,7 @@
 #include "net/third_party/quiche/src/quic/platform/api/quic_test.h"
 
 using ::testing::_;
+using ::testing::Eq;
 using ::testing::InSequence;
 using ::testing::Return;
 
@@ -157,7 +158,7 @@
                                 frame_type, Http3FrameLengths(header_length,
                                                               payload_length)));
       if (payload_length > 0) {
-        EXPECT_CALL(visitor_, OnUnknownFramePayload(data));
+        EXPECT_CALL(visitor_, OnUnknownFramePayload(Eq(data)));
       }
       EXPECT_CALL(visitor_, OnUnknownFrameEnd());