[gin] Fire observer after added when recording is in progress.

gin/v8_platform.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gin/public/v8_platform.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/sys_info.h"
 #include "base/threading/worker_pool.h"
@@ skipping 199 matching lines @@
   }
 
   void OnTraceLogDisabled() final {
     base::AutoLock lock(mutex_);
     for (auto o : observers_) {
       o->OnTraceDisabled();
     }
   }
 
   void AddObserver(v8::Platform::TraceStateObserver* observer) {
-    base::AutoLock lock(mutex_);
-    DCHECK(!observers_.count(observer));
-    observers_.insert(observer);
-    if (observers_.size() == 1) {
-      base::trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(this);
+    {
+      base::AutoLock lock(mutex_);
+      DCHECK(!observers_.count(observer));
+      observers_.insert(observer);

[alph, 2017/01/25 22:39:06]

Can you please move this line past 225. Just to be on the safe side if/when
AddEnabledStateObserver also implements similar logic.

[lpy, 2017/01/25 23:11:15]

I don't understand here, what do you mean similar logic? Do you mean if
`AddEnabledStateObserver` fires observer when observer is being added and then
we are in dead lock here?

Moving `observers_.insert(observer)` past 225 means EnabledStateObserverImpl
won't add itself to observer list in TraceLog the first time when `AddObserver`
is called.

[alph, 2017/01/25 23:26:32]

My suggestion implied you change "observers_.size() == 1" to
"observers_.empty()"

[lpy, 2017/01/26 02:26:41]

Done.

+      if (observers_.size() == 1) {
+        base::trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(
+            this);
+      }
     }
+    // Fire the observer if recording is already in progress.
+    if (base::trace_event::TraceLog::GetInstance()->IsEnabled())
+      observer->OnTraceEnabled();
   }
 
   void RemoveObserver(v8::Platform::TraceStateObserver* observer) {
     base::AutoLock lock(mutex_);
     DCHECK(observers_.count(observer) == 1);
     observers_.erase(observer);
     if (observers_.empty()) {
       base::trace_event::TraceLog::GetInstance()->RemoveEnabledStateObserver(
           this);
     }
@@ skipping 15 matching lines @@
     v8::Platform::TraceStateObserver* observer) {
   g_trace_state_dispatcher.Get().AddObserver(observer);
 }
 
 void V8Platform::RemoveTraceStateObserver(
     v8::Platform::TraceStateObserver* observer) {
   g_trace_state_dispatcher.Get().RemoveObserver(observer);
 }
 
 }  // namespace gin