Bug 1137151: Marked destructor of |MemoryPressureWatcher| as protected, r=dhylands

widget/gonk/GonkMemoryPressureMonitoring.cpp

@@ -60,7 +60,7 @@ namespace {
  * between read()s, we sleep by Wait()'ing on a monitor, which we notify on
  * shutdown.
  */
-class MemoryPressureWatcher
+class MemoryPressureWatcher MOZ_FINAL
   : public nsIRunnable
   , public nsIObserver
 {
@@ -217,6 +217,9 @@ public:
     return NS_OK;
   }
 
+protected:
+  ~MemoryPressureWatcher() {}
+
 private:
   /**
    * Read from aLowMemFd, which we assume corresponds to the