Bug 1244883 - Add Nightly-/Aurora-only crash for AsyncTransactionWaiter timeouts - r=nical

gfx/2d/Logging.h

@@ -132,6 +132,7 @@ enum class LogReason : int {
   CannotDraw3D, // 20
   IncompatibleBasicTexturedEffect,
   InvalidFont,
+  AsyncTransactionTimeout,
   // End
   MustBeLessThanThis = 101,
 };

gfx/layers/ipc/AsyncTransactionTracker.cpp

@@ -34,6 +34,10 @@ AsyncTransactionWaiter::WaitComplete()
   if (mWaitCount > 0) {
     printf_stderr("Timeout of waiting transaction complete.");
   }
+
+  if (count == maxCount) {
+    gfxDevCrash(LogReason::AsyncTransactionTimeout) << "Bug 1244883: AsyncTransactionWaiter timed out.";
+  }
 }
 
 Atomic<uint64_t> AsyncTransactionTracker::sSerialCounter(0);