enable / disable Long Task instrumentation based on presence of LongTask observer

third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp

Index: third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
diff --git a/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp b/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
index 3e085f1dad921f58b49bdf0dda7b619061c1993c..bb0dc718a4cac5afa140b7dcfca9a1e55b896266 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
+++ b/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
@@ -16,11 +16,19 @@ namespace blink {
 InspectorWebPerfAgent::InspectorWebPerfAgent(InspectedFrames* inspectedFrames)
     : m_inspectedFrames(inspectedFrames)
 {
+}
+
+InspectorWebPerfAgent::~InspectorWebPerfAgent()
+{

[dgozman, 2016/09/17 01:11:00]

Let's either call disableObserver() from here or DCHECK we've been disabled.

[panicker, 2016/09/17 03:04:00]

How's this?

[panicker, 2016/09/18 17:49:59]

hmm it's not okay to access potentially finalized fields in dtor.
Were you concerned about the task-observers OR removeInspectorWebPerfAgent ?

[dgozman, 2016/09/19 17:55:59]

Both. I propose to have |enabled_| field, update it in
enableObserver/disableObserver and DCHECK(!enabled_) here.

[panicker, 2016/09/20 12:00:39]

Done.

+}
+
+void InspectorWebPerfAgent::enableObserver()
+{
     Platform::current()->currentThread()->addTaskTimeObserver(this);
     Platform::current()->currentThread()->addTaskObserver(this);
 }
 
-InspectorWebPerfAgent::~InspectorWebPerfAgent()
+void InspectorWebPerfAgent::disableObserver()
 {
     Platform::current()->currentThread()->removeTaskTimeObserver(this);
     Platform::current()->currentThread()->removeTaskObserver(this);