Remove use of the deprecated mx_current_time Fuchsia syscall

runtime/vm/os_thread_fuchsia.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"  // NOLINT
 #if defined(TARGET_OS_FUCHSIA)
 
 #include "vm/os_thread.h"
 #include "vm/os_thread_fuchsia.h"
 
@@ skipping 29 matching lines @@
     return result; \
   }
 #else
 #define RETURN_ON_PTHREAD_FAILURE(result) \
   if (result != 0) return result;
 #endif
 
 
 static void ComputeTimeSpecMicros(struct timespec* ts, int64_t micros) {
   // time in nanoseconds.
-  mx_time_t now = mx_current_time();
+  mx_time_t now = mx_time_get(MX_CLOCK_MONOTONIC);
   mx_time_t target = now + (micros * kNanosecondsPerMicrosecond);
   int64_t secs = target / kNanosecondsPerSecond;
   int64_t nanos = target - (secs * kNanosecondsPerSecond);
 
   ts->tv_sec = secs;
   ts->tv_nsec = nanos;
 }
 
 
 class ThreadStartData {
@@ skipping 361 matching lines @@
 void Monitor::NotifyAll() {
   // When running with assertions enabled we track the owner.
   ASSERT(IsOwnedByCurrentThread());
   int result = pthread_cond_broadcast(data_.cond());
   VALIDATE_PTHREAD_RESULT(result);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_FUCHSIA)