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

gin/v8_platform.cc

Index: gin/v8_platform.cc
diff --git a/gin/v8_platform.cc b/gin/v8_platform.cc
index 6e5491bff11801397e353cb371b1a9762fffb970..6be7b88d4f594be6895e142ada20e8da5077f265 100644
--- a/gin/v8_platform.cc
+++ b/gin/v8_platform.cc
@@ -217,12 +217,18 @@ class EnabledStateObserverImpl final
   }
 
   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) {