Refactor monotonic clock interface and use raw tick values in stopwatch

runtime/bin/utils_macos.cc

Index: runtime/bin/utils_macos.cc
diff --git a/runtime/bin/utils_macos.cc b/runtime/bin/utils_macos.cc
index e4d718ff2c03b3fa51d8fbe18c6211f812201d00..5ac414fb9b5ca399e7970403e4ba28d415d68365 100644
--- a/runtime/bin/utils_macos.cc
+++ b/runtime/bin/utils_macos.cc
@@ -74,7 +74,11 @@ bool ShellUtils::GetUtf8Argv(int argc, char** argv) {
   return false;
 }
 
+static mach_timebase_info_data_t timebase_info;
+
 void TimerUtils::InitOnce() {
+  kern_return_t kr = mach_timebase_info(&timebase_info);
+  ASSERT(KERN_SUCCESS == kr);
 }
 
 int64_t TimerUtils::GetCurrentMonotonicMillis() {
@@ -97,17 +101,7 @@ int64_t TimerUtils::GetCurrentMonotonicMicros() {
   origin += boottime.tv_usec;
   return now - origin;
 #else
-  static mach_timebase_info_data_t timebase_info;
-  if (timebase_info.denom == 0) {
-    // Zero-initialization of statics guarantees that denom will be 0 before
-    // calling mach_timebase_info.  mach_timebase_info will never set denom to
-    // 0 as that would be invalid, so the zero-check can be used to determine
-    // whether mach_timebase_info has already been called.  This is
-    // recommended by Apple's QA1398.
-    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.  Convert
   // to microseconds.
   int64_t result = mach_absolute_time() / kNanosecondsPerMicrosecond;