Internally measure isolate uptime with monotonic time.

runtime/vm/os_test.cc

 // Copyright (c) 2013, 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 "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/globals.h"
 #include "vm/os.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
 UNIT_TEST_CASE(Sleep) {
-  int64_t start_time = OS::GetCurrentTimeMillis();
-  int64_t sleep_time = 702;
-  OS::Sleep(sleep_time);
-  int64_t delta = OS::GetCurrentTimeMillis() - start_time;
-  const int kAcceptableSleepWakeupJitter = 200;  // Measured in milliseconds.
+  // All times measured in microseconds.
+  int64_t start_time = OS::GetCurrentMonotonicMicros();
+  int64_t sleep_time = 702000;
+  OS::SleepMicros(sleep_time);
+  int64_t delta = OS::GetCurrentMonotonicMicros() - start_time;
+  const int kAcceptableSleepWakeupJitter = 200000;
   EXPECT_GE(delta, sleep_time - kAcceptableSleepWakeupJitter);
   EXPECT_LE(delta, sleep_time + kAcceptableSleepWakeupJitter);
 }
 
 
 UNIT_TEST_CASE(SNPrint) {
   char buffer[256];
   int length;
   length = OS::SNPrint(buffer, 10, "%s", "foo");
   EXPECT_EQ(3, length);
@@ skipping 18 matching lines @@
 
 
 UNIT_TEST_CASE(OsFuncs) {
   EXPECT(Utils::IsPowerOfTwo(OS::ActivationFrameAlignment()));
   EXPECT(Utils::IsPowerOfTwo(OS::PreferredCodeAlignment()));
   int procs = OS::NumberOfAvailableProcessors();
   EXPECT_LE(1, procs);
 }
 
 }  // namespace dart