Bug 1366812 - Initialize TimeoutManager::mThrottleTrackingTimeouts to false; r=smaug

This way we won't rely on code which may have potentially not run yet.

dom/base/TimeoutManager.cpp

@@ -306,7 +306,7 @@ TimeoutManager::TimeoutManager(nsGlobalWindow& aWindow)
     mRunningTimeout(nullptr),
     mIdleCallbackTimeoutCounter(1),
     mBackPressureDelayMS(0),
-    mThrottleTrackingTimeouts(gTrackingTimeoutThrottlingDelay <= 0)
+    mThrottleTrackingTimeouts(false)
 {
   MOZ_DIAGNOSTIC_ASSERT(aWindow.IsInnerWindow());