Use a monotonic clock in the implementation of Stopwatch.

runtime/vm/profiler.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/address_sanitizer.h"
 #include "platform/memory_sanitizer.h"
 #include "platform/utils.h"
 
 #include "vm/allocation.h"
 #include "vm/atomic.h"
@@ skipping 802 matching lines @@
 }
 
 
 static Sample* SetupSample(Thread* thread,
                            SampleBuffer* sample_buffer,
                            ThreadId tid) {
   ASSERT(thread != NULL);
   Isolate* isolate = thread->isolate();
   ASSERT(sample_buffer != NULL);
   Sample* sample = sample_buffer->ReserveSample();
-  sample->Init(isolate, OS::GetCurrentTraceMicros(), tid);
+  sample->Init(isolate, OS::GetCurrentMonotonicMicros(), tid);
   uword vm_tag = thread->vm_tag();
 #if defined(USING_SIMULATOR)
   // When running in the simulator, the runtime entry function address
   // (stored as the vm tag) is the address of a redirect function.
   // Attempt to find the real runtime entry function address and use that.
   uword redirect_vm_tag = Simulator::FunctionForRedirect(vm_tag);
   if (redirect_vm_tag != 0) {
     vm_tag = redirect_vm_tag;
   }
 #endif
@@ skipping 527 matching lines @@
   }
 }
 
 
 ProcessedSampleBuffer::ProcessedSampleBuffer()
     : code_lookup_table_(new CodeLookupTable(Thread::Current())) {
   ASSERT(code_lookup_table_ != NULL);
 }
 
 }  // namespace dart