Update {virtual,override} to follow C++11 style in components.

components/nacl/common/nacl_debug_exception_handler_win.cc

Index: components/nacl/common/nacl_debug_exception_handler_win.cc
diff --git a/components/nacl/common/nacl_debug_exception_handler_win.cc b/components/nacl/common/nacl_debug_exception_handler_win.cc
index 68e3a666cc30791a7854908fdcf3a57b4ff5deb2..d7c1bb8e68c1f06eaa959edfe0f00d7e478c8f9f 100644
--- a/components/nacl/common/nacl_debug_exception_handler_win.cc
+++ b/components/nacl/common/nacl_debug_exception_handler_win.cc
@@ -23,7 +23,7 @@ class DebugExceptionHandler : public base::PlatformThread::Delegate {
         message_loop_(message_loop),
         on_connected_(on_connected) {}
 
-  virtual void ThreadMain() override {
+  void ThreadMain() override {
     // In the Windows API, the set of processes being debugged is
     // thread-local, so we have to attach to the process (using
     // DebugActiveProcess()) on the same thread on which