Mojo: Convert OVERRIDE -> override in mojo/{embedder,system}.

mojo/system/waiter_unittest.cc

Index: mojo/system/waiter_unittest.cc
diff --git a/mojo/system/waiter_unittest.cc b/mojo/system/waiter_unittest.cc
index 4656927c507dc738568df6851193b10cb0f25453..95993b24b3a1dc28bcda367dd6e57e8974765a7e 100644
--- a/mojo/system/waiter_unittest.cc
+++ b/mojo/system/waiter_unittest.cc
@@ -61,7 +61,7 @@ class WaitingThread : public base::SimpleThread {
   Waiter* waiter() { return &waiter_; }
 
  private:
-  virtual void Run() OVERRIDE {
+  virtual void Run() override {
     test::Stopwatch stopwatch;
     MojoResult result;
     uint32_t context = static_cast<uint32_t>(-1);