Fix build on windows

uid_t is now signed on windows, since 92e6c082c61b("Update uid_t on
Windows to be signed").

Change-Id: Ib5bd9738bcf3d3468cf96853c8d7d4bf9b616931
diff --git a/src/tracing/service/trace_buffer_unittest.cc b/src/tracing/service/trace_buffer_unittest.cc
index 906b0df..65cb425 100644
--- a/src/tracing/service/trace_buffer_unittest.cc
+++ b/src/tracing/service/trace_buffer_unittest.cc
@@ -812,24 +812,24 @@
   TraceBuffer::PacketSequenceProperties sequence_properties;
   ASSERT_THAT(ReadPacket(&sequence_properties),
               ElementsAre(FakePacketFragment(10, 'a')));
-  ASSERT_EQ(11u, sequence_properties.producer_uid_trusted());
+  ASSERT_EQ(static_cast<uid_t>(11), sequence_properties.producer_uid_trusted());
 
   ASSERT_THAT(
       ReadPacket(&sequence_properties),
       ElementsAre(FakePacketFragment(10, 'b'), FakePacketFragment(10, 'e')));
-  ASSERT_EQ(11u, sequence_properties.producer_uid_trusted());
+  ASSERT_EQ(static_cast<uid_t>(11), sequence_properties.producer_uid_trusted());
 
   ASSERT_THAT(ReadPacket(&sequence_properties),
               ElementsAre(FakePacketFragment(10, 'f')));
-  ASSERT_EQ(11u, sequence_properties.producer_uid_trusted());
+  ASSERT_EQ(static_cast<uid_t>(11), sequence_properties.producer_uid_trusted());
 
   ASSERT_THAT(ReadPacket(&sequence_properties),
               ElementsAre(FakePacketFragment(10, 'c')));
-  ASSERT_EQ(22u, sequence_properties.producer_uid_trusted());
+  ASSERT_EQ(static_cast<uid_t>(22), sequence_properties.producer_uid_trusted());
 
   ASSERT_THAT(ReadPacket(&sequence_properties),
               ElementsAre(FakePacketFragment(10, 'd')));
-  ASSERT_EQ(22u, sequence_properties.producer_uid_trusted());
+  ASSERT_EQ(static_cast<uid_t>(22), sequence_properties.producer_uid_trusted());
 
   ASSERT_THAT(ReadPacket(), IsEmpty());
 }