Fix iOS implementation of |GetCurrentMonotonicMicros|.

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 5ac414fb9b5ca399e7970403e4ba28d415d68365..eea4cb750b077503736bc228d18a32d445e5163c 100644
--- a/runtime/bin/utils_macos.cc
+++ b/runtime/bin/utils_macos.cc
@@ -13,6 +13,10 @@
 #include <sys/time.h>  // NOLINT
 #include <time.h>  // NOLINT
 
+#if TARGET_OS_IOS
+#include <sys/sysctl.h>  // NOLINT
+#endif
+
 #include "bin/utils.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ -85,6 +89,20 @@ int64_t TimerUtils::GetCurrentMonotonicMillis() {
   return GetCurrentMonotonicMicros() / 1000;
 }
 
+#if TARGET_OS_IOS
+
+static int64_t GetCurrentTimeMicros() {
+  // gettimeofday has microsecond resolution.
+  struct timeval tv;
+  if (gettimeofday(&tv, NULL) < 0) {
+    UNREACHABLE();
+    return 0;
+  }
+  return (static_cast<int64_t>(tv.tv_sec) * 1000000) + tv.tv_usec;
+}
+
+#endif  // TARGET_OS_IOS
+
 int64_t TimerUtils::GetCurrentMonotonicMicros() {
 #if TARGET_OS_IOS
   // On iOS mach_absolute_time stops while the device is sleeping. Instead use