use millis to protect against potential overflow

test/core/util/test_config.h

@@ -56,7 +56,7 @@ extern double g_fixture_slowdown_factor;
 
 #define GRPC_TIMEOUT_SECONDS_TO_DEADLINE(x)                                \
   gpr_time_add(gpr_now(GPR_CLOCK_MONOTONIC),                               \
-               gpr_time_from_micros(GRPC_TEST_SLOWDOWN_FACTOR * 1e6 * (x), \
+               gpr_time_from_millis(GRPC_TEST_SLOWDOWN_FACTOR * 1e3 * (x), \
                                     GPR_TIMESPAN))
 
 #define GRPC_TIMEOUT_MILLIS_TO_DEADLINE(x)                                 \