Remove use of the deprecated mx_current_time Fuchsia syscall

runtime/vm/os_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 "vm/globals.h"
 #if defined(TARGET_OS_FUCHSIA)
 
 #include "vm/os.h"
 
 #include <errno.h>
@@ skipping 57 matching lines @@
   return static_cast<int>(-timezone);
 }
 
 
 int64_t OS::GetCurrentTimeMillis() {
   return GetCurrentTimeMicros() / 1000;
 }
 
 
 int64_t OS::GetCurrentTimeMicros() {
-  return mx_current_time() / 1000;
+  return mx_time_get(MX_CLOCK_MONOTONIC) / 1000;
 }
 
 
 int64_t OS::GetCurrentMonotonicTicks() {
-  return mx_current_time();
+  return mx_time_get(MX_CLOCK_MONOTONIC);
 }
 
 
 int64_t OS::GetCurrentMonotonicFrequency() {
   return kNanosecondsPerSecond;
 }
 
 
 int64_t OS::GetCurrentMonotonicMicros() {
   int64_t ticks = GetCurrentMonotonicTicks();
@@ skipping 215 matching lines @@
 }
 
 
 void OS::Exit(int code) {
   UNIMPLEMENTED();
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_FUCHSIA)