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

src/counters-inl.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COUNTERS_INL_H_
 #define V8_COUNTERS_INL_H_
 
 #include "src/counters.h"
 
 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)) {
     Initialize(isolate->counters()->runtime_call_stats(), counter_id);
   }
 }
 
 RuntimeCallTimerScope::RuntimeCallTimerScope(
     HeapObject* heap_object, RuntimeCallStats::CounterId counter_id) {
   RuntimeCallTimerScope(heap_object->GetIsolate(), counter_id);
 }
 
 RuntimeCallTimerScope::RuntimeCallTimerScope(
     RuntimeCallStats* stats, RuntimeCallStats::CounterId counter_id) {
   if (V8_UNLIKELY(FLAG_runtime_stats)) {
     Initialize(stats, counter_id);
   }
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COUNTERS_INL_H_