Bug 1408294 - Assert that we don't underrun globally. r=padenot

MozReview-Commit-ID: 1vEN1K1TK5n

--HG--
extra : rebase_source : e2bcc28d52b28e741e8a114db4cee9880abf6562

dom/media/GraphDriver.cpp

@@ -960,7 +960,8 @@ AudioCallbackDriver::DataCallback(const AudioDataValue* aInputBuffer,
   mCurrentTimeStamp = TimeStamp::Now();
 
   if (stateComputedTime < mIterationEnd) {
-    LOG(LogLevel::Warning, ("Media graph global underrun detected"));
+    LOG(LogLevel::Error, ("Media graph global underrun detected"));
+    MOZ_ASSERT_UNREACHABLE("We should not underrun in full duplex");
     mIterationEnd = stateComputedTime;
   }