Fix bug with runtime-call-stats timers

RuntimeCallTimers were not properly stopped and this made a DCHECK
in the Debug version fail.

R=cbruni@chromium.org
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/1955943002
Cr-Commit-Position: refs/heads/master@{#36097}

src/counters.h

@@ -505,6 +505,7 @@ class RuntimeCallTimer {
 
   inline RuntimeCallTimer* Stop() {
     base::TimeDelta delta = timer_.Elapsed();
+    timer_.Stop();
     counter_->time += delta;
     if (parent_ != NULL) {
       parent_->AdjustForSubTimer(delta);