Add a QuicChromiumClock and make QuicClock abstract to match internal code.

net/quic/quartc/quartc_session_test.cc

Index: net/quic/quartc/quartc_session_test.cc
diff --git a/net/quic/quartc/quartc_session_test.cc b/net/quic/quartc/quartc_session_test.cc
index 788a2cd5c0fb0173b8068ff240e11a8ca161f397..6617ad4273687005ea8e9ae51f50128578e521c5 100644
--- a/net/quic/quartc/quartc_session_test.cc
+++ b/net/quic/quartc/quartc_session_test.cc
@@ -18,6 +18,7 @@
 #include "net/quic/core/quic_crypto_client_stream.h"
 #include "net/quic/core/quic_crypto_server_stream.h"
 #include "net/quic/core/quic_simple_buffer_allocator.h"
+#include "net/quic/platform/impl/quic_chromium_clock.h"
 #include "net/quic/quartc/quartc_alarm_factory.h"
 #include "net/quic/quartc/quartc_packet_writer.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -448,7 +449,7 @@ class QuartcSessionTest : public ::testing::Test,
  protected:
   std::unique_ptr<QuicAlarmFactory> alarm_factory_;
   SimpleBufferAllocator buffer_allocator_;
-  QuicClock clock_;
+  QuicChromiumClock clock_;
 
   std::unique_ptr<FakeTransportChannel> client_channel_;
   std::unique_ptr<FakeTransportChannel> server_channel_;