Change virtual to override in devtools generator code.

Changes Client destructor to be override instead of virtual to conform with chromium-style.

BUG=417463

Review URL: https://codereview.chromium.org/1108613002

Cr-Commit-Position: refs/heads/master@{#326842}

content/browser/devtools/protocol/devtools_protocol_handler_generator.py

@@ -207,7 +207,7 @@ namespace ${domain} {
 class Client : public DevToolsProtocolClient {
  public:
   explicit Client(const RawMessageCallback& raw_message_callback);
-  virtual ~Client();
+  ~Client() override;
 
 ${methods}\
 };