Previously, a call to Dart_TimelineGetMicros() before a call to
Dart_Initialize() resulted in a crash. This was fixed in
dart-lang/sdk@7434bcad57b567c4b62d48b11b99c323cb245d66.

Related:
* flutter/flutter#4006: SkyShell.app on Mac crashes on startup
* dart-lang/sdk#26486:  [dart_tools_api.h] Dart_TimelineGetMicros crashes on Mac if called before Dart_Initialize