Bug 1155303 - Add telemetry for async DeferredFinalize max pause. r=smaug

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -59,6 +59,7 @@
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/AutoRestore.h"
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/Telemetry.h"
 #include "mozilla/dom/BindingUtils.h"
 #include "mozilla/DebuggerOnGCRunnable.h"
 #include "mozilla/dom/DOMJSClass.h"
@@ -1166,6 +1167,7 @@ IncrementalFinalizeRunnable::Run()
     return NS_OK;
   }
 
+  TimeStamp start = TimeStamp::Now();
   ReleaseNow(true);
 
   if (mDeferredFinalizeFunctions.Length()) {
@@ -1175,6 +1177,9 @@ IncrementalFinalizeRunnable::Run()
     }
   }
 
+  uint32_t duration = (uint32_t)((TimeStamp::Now() - start).ToMilliseconds());
+  Telemetry::Accumulate(Telemetry::DEFERRED_FINALIZE_ASYNC, duration);
+
   return NS_OK;
 }