[CrOS Tether] ProximityAuth WebUI improvement: show the local device's ID.

chrome/browser/signin/chrome_proximity_auth_client.h

Index: chrome/browser/signin/chrome_proximity_auth_client.h
diff --git a/chrome/browser/signin/chrome_proximity_auth_client.h b/chrome/browser/signin/chrome_proximity_auth_client.h
index 463f7c8709fbd0e1fbef41fa804777c48f28040a..c859487de7cc597e3c5b8b27638de01a8269bc64 100644
--- a/chrome/browser/signin/chrome_proximity_auth_client.h
+++ b/chrome/browser/signin/chrome_proximity_auth_client.h
@@ -42,6 +42,7 @@ class ChromeProximityAuthClient : public proximity_auth::ProximityAuthClient {
       const std::string& remote_public_key,
       const std::string& nonce,
       base::Callback<void(const std::string& challenge)> callback) override;
+  std::string GetLocalDevicePublicKey() override;
 
  private:
   cryptauth::CryptAuthService* GetCryptAuthService();