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

mojo/system/message_pipe_dispatcher_unittest.cc

Index: mojo/system/message_pipe_dispatcher_unittest.cc
diff --git a/mojo/system/message_pipe_dispatcher_unittest.cc b/mojo/system/message_pipe_dispatcher_unittest.cc
index bd55ecf56ae998da6265130c38cfa51b957427df..f0eb1eb41c1d1bf0a5263bd2b97afafcc44a240b 100644
--- a/mojo/system/message_pipe_dispatcher_unittest.cc
+++ b/mojo/system/message_pipe_dispatcher_unittest.cc
@@ -531,7 +531,7 @@ class WriterThread : public base::SimpleThread {
   virtual ~WriterThread() { Join(); }
 
  private:
-  virtual void Run() OVERRIDE {
+  virtual void Run() override {
     // Make some data to write.
     unsigned char buffer[kMaxMessageSize];
     for (size_t i = 0; i < kMaxMessageSize; i++)
@@ -584,7 +584,7 @@ class ReaderThread : public base::SimpleThread {
   virtual ~ReaderThread() { Join(); }
 
  private:
-  virtual void Run() OVERRIDE {
+  virtual void Run() override {
     unsigned char buffer[kMaxMessageSize];
     Waiter w;
     HandleSignalsState hss;