[counters] RuntimeStats: fix wrong bookkeeping when dynamically changing counters.

src/counters-inl.h

Index: src/counters-inl.h
diff --git a/src/counters-inl.h b/src/counters-inl.h
index 7219ef778a6ea6a06ce25ad457b7a1299c5d7194..ce77806cdcfa4d5117da06aae41edcc5bea13e83 100644
--- a/src/counters-inl.h
+++ b/src/counters-inl.h
@@ -10,6 +10,57 @@
 namespace v8 {
 namespace internal {
 
+void RuntimeCallTimer::Start(RuntimeCallCounter* counter,
+                             RuntimeCallTimer* parent) {
+  DCHECK(!IsStarted());
+  counter_ = counter;
+  parent_.SetValue(parent);
+  if (FLAG_runtime_stats ==
+      v8::tracing::TracingCategoryObserver::ENABLED_BY_SAMPLING) {
+    return;
+  }
+  base::TimeTicks now = Now();
+  if (parent) parent->Pause(now);
+  Resume(now);
+  DCHECK(IsStarted());
+}
+
+void RuntimeCallTimer::Pause(base::TimeTicks now) {
+  DCHECK(IsStarted());
+  elapsed_ += (now - start_ticks_);
+  start_ticks_ = base::TimeTicks();
+}
+
+void RuntimeCallTimer::Resume(base::TimeTicks now) {
+  DCHECK(!IsStarted());
+  start_ticks_ = now;
+}
+
+RuntimeCallTimer* RuntimeCallTimer::Stop() {
+  if (!IsStarted()) return parent();
+  base::TimeTicks now = Now();
+  Pause(now);
+  counter_->Increment();
+  CommitTimeToCounter();
+
+  RuntimeCallTimer* parent_timer = parent();
+  if (parent_timer) {
+    parent_timer->Resume(now);
+  }
+  return parent_timer;
+}
+
+void RuntimeCallTimer::CommitTimeToCounter() {
+  counter_->Add(elapsed_);
+  elapsed_ = base::TimeDelta();
+}
+
+bool RuntimeCallTimer::IsStarted() { return start_ticks_ != base::TimeTicks(); }
+
+base::TimeTicks RuntimeCallTimer::Now() {
+  return base::TimeTicks::HighResolutionNow();
+}
+
 RuntimeCallTimerScope::RuntimeCallTimerScope(
     Isolate* isolate, RuntimeCallStats::CounterId counter_id) {
   if (V8_UNLIKELY(FLAG_runtime_stats)) {