Long tasks: add a trace event for long tasks

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 a60c520b94f94b3757d865b804b8e0504dd77656..33a85e4e5c7e9990b2790504ff9483dc6e451c3a 100644
--- a/third_party/WebKit/Source/core/timing/Performance.cpp
+++ b/third_party/WebKit/Source/core/timing/Performance.cpp
@@ -46,7 +46,7 @@
 #include "platform/loader/fetch/ResourceTimingInfo.h"
 #include "platform/RuntimeEnabledFeatures.h"
 
-static const double kLongTaskThreshold = 0.05;
+static const double kLongTaskObserverThreshold = 0.05;
 
 static const char kUnknownAttribution[] = "unknown";
 static const char kAmbiguousAttribution[] = "multiple-contexts";
@@ -158,7 +158,7 @@ void Performance::UpdateLongTaskInstrumentation() {
     UseCounter::Count(&GetFrame()->LocalFrameRoot(),
                       WebFeature::kLongTaskObserver);
     GetFrame()->GetPerformanceMonitor()->Subscribe(
-        PerformanceMonitor::kLongTask, kLongTaskThreshold, this);
+        PerformanceMonitor::kLongTask, kLongTaskObserverThreshold, this);
   } else {
     GetFrame()->GetPerformanceMonitor()->UnsubscribeAll(this);
   }