Oilpan: Trace ThreadState::performIdleGC() function for better debuggability.

Source/platform/heap/ThreadState.cpp

Index: Source/platform/heap/ThreadState.cpp
diff --git a/Source/platform/heap/ThreadState.cpp b/Source/platform/heap/ThreadState.cpp
index 2c89ff49081d07f3b55bd8edae009222d8e59e3b..73afe55fb9d405a2dd345e901dbcd85afe6609e6 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -679,6 +679,7 @@ void ThreadState::performIdleGC(double deadlineSeconds)
         return;
 
     double idleDeltaInSeconds = deadlineSeconds - Platform::current()->monotonicallyIncreasingTime();
+    TRACE_EVENT2("blink_gc", "ThreadState::performIdleGC", "idleDeltaInSeconds", idleDeltaInSeconds, "estimatedMarkingTime", Heap::estimatedMarkingTime());
     if (idleDeltaInSeconds <= Heap::estimatedMarkingTime() && !Platform::current()->currentThread()->scheduler()->canExceedIdleDeadlineIfRequired()) {
         // If marking is estimated to take longer than the deadline and we can't
         // exceed the deadline, then reschedule for the next idle period.