Add OriginTrial flag for Long Task Observer

third_party/WebKit/Source/core/timing/Performance.cpp

Index: third_party/WebKit/Source/core/timing/Performance.cpp
diff --git a/third_party/WebKit/Source/core/timing/Performance.cpp b/third_party/WebKit/Source/core/timing/Performance.cpp
index 4d7ebcccf09214341b4dbe144e8f8454664639b1..a2521509bdcf3b00b84c86b8bd8a4579ad4f7685 100644
--- a/third_party/WebKit/Source/core/timing/Performance.cpp
+++ b/third_party/WebKit/Source/core/timing/Performance.cpp
@@ -36,6 +36,7 @@
 #include "core/inspector/InspectedFrames.h"
 #include "core/inspector/InspectorWebPerfAgent.h"
 #include "core/loader/DocumentLoader.h"
+#include "core/origin_trials/OriginTrials.h"
 #include "core/timing/PerformanceTiming.h"
 
 namespace blink {
@@ -97,6 +98,9 @@ PerformanceTiming* Performance::timing() const
 void Performance::updateLongTaskInstrumentation()
 {
     if (hasObserverFor(PerformanceEntry::LongTask) && !m_longTaskInspectorAgent) {
+        if (!frame() || !frame()->document()
+            || !OriginTrials::longTaskObserverEnabled(frame()->document()))
+            return;
         m_longTaskInspectorAgent = new InspectorWebPerfAgent(
             InspectedFrames::create(frame()));
         m_longTaskInspectorAgent->enable();