Update GC stats, ThreadPool, Timer and ScopedTimer to use monotonic time.

runtime/vm/heap.cc

 // Copyright (c) 2012, 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 "vm/heap.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
@@ skipping 675 matching lines @@
 }
 #endif  // PRODUCT
 
 
 void Heap::RecordBeforeGC(Space space, GCReason reason) {
   ASSERT((space == kNew && gc_new_space_in_progress_) ||
          (space == kOld && gc_old_space_in_progress_));
   stats_.num_++;
   stats_.space_ = space;
   stats_.reason_ = reason;
-  stats_.before_.micros_ = OS::GetCurrentTimeMicros();
+  stats_.before_.micros_ = OS::GetCurrentMonotonicMicros();
   stats_.before_.new_ = new_space_.GetCurrentUsage();
   stats_.before_.old_ = old_space_.GetCurrentUsage();
   stats_.times_[0] = 0;
   stats_.times_[1] = 0;
   stats_.times_[2] = 0;
   stats_.times_[3] = 0;
   stats_.data_[0] = 0;
   stats_.data_[1] = 0;
   stats_.data_[2] = 0;
   stats_.data_[3] = 0;
 }
 
 
 void Heap::RecordAfterGC(Space space) {
-  stats_.after_.micros_ = OS::GetCurrentTimeMicros();
+  stats_.after_.micros_ = OS::GetCurrentMonotonicMicros();
   int64_t delta = stats_.after_.micros_ - stats_.before_.micros_;
   if (stats_.space_ == kNew) {
     new_space_.AddGCTime(delta);
     new_space_.IncrementCollections();
   } else {
     old_space_.AddGCTime(delta);
     old_space_.IncrementCollections();
   }
   stats_.after_.new_ = new_space_.GetCurrentUsage();
   stats_.after_.old_ = old_space_.GetCurrentUsage();
@@ skipping 121 matching lines @@
   Dart::vm_isolate()->heap()->WriteProtect(false);
 }
 
 
 WritableVMIsolateScope::~WritableVMIsolateScope() {
   ASSERT(Dart::vm_isolate()->heap()->UsedInWords(Heap::kNew) == 0);
   Dart::vm_isolate()->heap()->WriteProtect(true);
 }
 
 }  // namespace dart