[RuntimeCallStats] Fix reset scope for tracing

https://codereview.chromium.org/2296243002/ introduced 2 minor bugs
related to the Reset scope.

The tracing version requires that we reset the counters everytime we
start a new top level trace event, unless the top level one is not
really a top level (i.e. has the right type but called in a nested way)

Bugs are:
1- Reseting was guarded behind a check for the runtime call stats
version only.
2- We never set that we are already inside a scope, so the nested
case would fail as well.

R=lpy@chromium.org, cbruni@chromium.org
BUG=642373

Review-Url: https://codereview.chromium.org/2311033002
Cr-Commit-Position: refs/heads/master@{#39214}

src/counters.cc

@@ -338,7 +338,9 @@ void RuntimeCallStats::Print(std::ostream& os) {
 }
 
 void RuntimeCallStats::Reset() {
-  if (!FLAG_runtime_call_stats) return;
+  if (!FLAG_runtime_call_stats &&
+      !TRACE_EVENT_RUNTIME_CALL_STATS_TRACING_ENABLED())
+    return;
 #define RESET_COUNTER(name) this->name.Reset();
   FOR_EACH_MANUAL_COUNTER(RESET_COUNTER)
 #undef RESET_COUNTER
@@ -358,6 +360,8 @@ void RuntimeCallStats::Reset() {
 #define RESET_COUNTER(name) this->Handler_##name.Reset();
   FOR_EACH_HANDLER_COUNTER(RESET_COUNTER)
 #undef RESET_COUNTER
+
+  in_use_ = true;
 }
 
 const char* RuntimeCallStats::Dump() {

src/counters.h

@@ -804,6 +804,7 @@ class RuntimeCallStats {
   size_t len_ = 0;
   // Counter to track recursive time events.
   RuntimeCallTimer* current_timer_ = NULL;
+  // Used to track nested tracing scopes.
   bool in_use_;
 };