Bug 1331495 - Add an operator<< overload for Maybe. r=froydnj

MozReview-Commit-ID: 8TcYoikeCvR

--HG--
extra : rebase_source : 591e3c635ae5521418105e2ad1fc2672143eceeb

mfbt/Maybe.h

@@ -16,6 +16,7 @@
 #include "mozilla/TypeTraits.h"
 
 #include <new>  // for placement new
+#include <ostream>
 #include <type_traits>
 
 namespace mozilla {
@@ -452,6 +453,17 @@ public:
     ::new (mStorage.addr()) T(Forward<Args>(aArgs)...);
     mIsSome = true;
   }
+
+  friend std::ostream&
+  operator<<(std::ostream& aStream, const Maybe<T>& aMaybe)
+  {
+    if (aMaybe) {
+      aStream << aMaybe.ref();
+    } else {
+      aStream << "<Nothing>";
+    }
+    return aStream;
+  }
 };
 
 /*