chromecast: tracing: Fix chromium-style warnings

../../chromecast/tracing/tracing_service_main.cc:96:28: error: [chromium-style] Overriding method must be marked with 'override' or 'final'.
  virtual ~TraceCopyTask() {}
                           ^
                            override
../../chromecast/tracing/tracing_service_main.cc:96:3: error: [chromium-style] 'virtual' will be redundant; 'override' implies 'virtual'.
  virtual ~TraceCopyTask() {}
  ^~~~~~~~
../../chromecast/tracing/tracing_service_main.cc:181:30: error: [chromium-style] Overriding method must be marked with 'override' or 'final'.
  virtual ~TraceConnection() {}
                             ^
                              override
../../chromecast/tracing/tracing_service_main.cc:181:3: error: [chromium-style] 'virtual' will be redundant; 'override' implies 'virtual'.
  virtual ~TraceConnection() {}
  ^~~~~~~~
../../chromecast/tracing/tracing_service_main.cc:339:29: error: [chromium-style] Overriding method must be marked with 'override' or 'final'.
  virtual ~TracingService() {}
                            ^
                             override
../../chromecast/tracing/tracing_service_main.cc:339:3: error: [chromium-style] 'virtual' will be redundant; 'override' implies 'virtual'.
  virtual ~TracingService() {}
  ^~~~~~~~
6 errors generated.

BUG=b/31079742

Change-Id: I8cc22c845599662e9a6088328933e67cd4ebf490
Reviewed-on: https://chromium-review.googlesource.com/814218
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Doug Steedman <dougsteed@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522453}

chromecast/tracing/tracing_service_main.cc

@@ -93,7 +93,7 @@ class TraceCopyTask : public base::MessagePumpLibevent::Watcher {
         out_fd_(std::move(out_fd)),
         out_watcher_(FROM_HERE),
         callback_(std::move(callback)) {}
-  virtual ~TraceCopyTask() {}
+  ~TraceCopyTask() override {}
 
   void Start() {
     base::MessageLoopForIO::current()->WatchFileDescriptor(
@@ -178,7 +178,7 @@ class TraceConnection : public base::MessagePumpLibevent::Watcher {
         connection_watcher_(FROM_HERE),
         callback_(std::move(callback)),
         weak_ptr_factory_(this) {}
-  virtual ~TraceConnection() {}
+  ~TraceConnection() override {}
 
   void Init() {
     base::MessageLoopForIO::current()->WatchFileDescriptor(
@@ -336,7 +336,7 @@ class TracingService : public base::MessagePumpLibevent::Watcher {
  public:
   TracingService()
       : server_socket_watcher_(FROM_HERE), weak_ptr_factory_(this) {}
-  virtual ~TracingService() {}
+  ~TracingService() override {}
 
   bool Init() {
     server_socket_ = CreateServerSocket();