Allow Dart_TimelineGetMicros to be called before Dart_Initialize on Mac

runtime/vm/os_macos.cc

 // Copyright (c) 2012, 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_MACOS)
 
 #include "vm/os.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 91 matching lines @@
   struct timeval boottime;
   int mib[2] = {CTL_KERN, KERN_BOOTTIME};
   size_t size = sizeof(boottime);
   int kr = sysctl(mib, sizeof(mib) / sizeof(mib[0]), &boottime, &size, NULL, 0);
   ASSERT(KERN_SUCCESS == kr);
   int64_t now = GetCurrentTimeMicros();
   int64_t origin = boottime.tv_sec * kMicrosecondsPerSecond;
   origin += boottime.tv_usec;
   return now - origin;
 #else
+  if (timebase_info.denom == 0) {
+    kern_return_t kr = mach_timebase_info(&timebase_info);
+    ASSERT(KERN_SUCCESS == kr);
+  }
   ASSERT(timebase_info.denom != 0);
   // timebase_info converts absolute time tick units into nanoseconds.
   int64_t result = mach_absolute_time();
   result *= timebase_info.numer;
   result /= timebase_info.denom;
   return result;
 #endif  // TARGET_OS_IOS
 }
 
 
@@ skipping 300 matching lines @@
 }
 
 
 void OS::InitOnce() {
   // TODO(5411554): For now we check that initonce is called only once,
   // Once there is more formal mechanism to call InitOnce we can move
   // this check there.
   static bool init_once_called = false;
   ASSERT(init_once_called == false);
   init_once_called = true;
-  kern_return_t kr = mach_timebase_info(&timebase_info);
-  ASSERT(KERN_SUCCESS == kr);
 }
 
 
 void OS::Shutdown() {
 }
 
 
 void OS::Abort() {
   abort();
 }
 
 
 void OS::Exit(int code) {
   exit(code);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)