Change QuicWallTime to have microsecond granularity.

net/tools/quic/quic_epoll_clock_test.cc

Index: net/tools/quic/quic_epoll_clock_test.cc
diff --git a/net/tools/quic/quic_epoll_clock_test.cc b/net/tools/quic/quic_epoll_clock_test.cc
index 1ed1d15c1d7eaa6d541239c240b113c6bb90dbbf..8fe492f2acf57883269bf34578f1c52f3f9e70e4 100644
--- a/net/tools/quic/quic_epoll_clock_test.cc
+++ b/net/tools/quic/quic_epoll_clock_test.cc
@@ -18,10 +18,18 @@ TEST(QuicEpollClockTest, ApproximateNowInUsec) {
   epoll_server.set_now_in_usec(1000000);
   EXPECT_EQ(1000000,
             clock.ApproximateNow().Subtract(QuicTime::Zero()).ToMicroseconds());
+  EXPECT_EQ(1u, clock.WallNow().ToUNIXSeconds());
+  EXPECT_EQ(1000000u, clock.WallNow().ToUNIXMicroseconds());
 
   epoll_server.AdvanceBy(5);
   EXPECT_EQ(1000005,
             clock.ApproximateNow().Subtract(QuicTime::Zero()).ToMicroseconds());
+  EXPECT_EQ(1u, clock.WallNow().ToUNIXSeconds());
+  EXPECT_EQ(1000005u, clock.WallNow().ToUNIXMicroseconds());
+
+  epoll_server.AdvanceBy(10 * 1000000);
+  EXPECT_EQ(11u, clock.WallNow().ToUNIXSeconds());
+  EXPECT_EQ(11000005u, clock.WallNow().ToUNIXMicroseconds());
 }
 
 TEST(QuicEpollClockTest, NowInUsec) {