Pass Device ID in the oauth2/token request. Keep Device ID in local state on Chrome OS.

chrome/browser/signin/chrome_signin_client.h

Index: chrome/browser/signin/chrome_signin_client.h
diff --git a/chrome/browser/signin/chrome_signin_client.h b/chrome/browser/signin/chrome_signin_client.h
index 016bf5b105328e9bd6b0f387475a9bc58c9d99bb..34003178cf35b34239ff9cccde78387e25a61540 100644
--- a/chrome/browser/signin/chrome_signin_client.h
+++ b/chrome/browser/signin/chrome_signin_client.h
@@ -33,6 +33,10 @@ class ChromeSigninClient
   static bool ProfileAllowsSigninCookies(Profile* profile);
   static bool SettingsAllowSigninCookies(CookieSettings* cookie_settings);
 
+  // If |for_ephemeral| is true, special kind of device ID for ephemeral users
+  // is generated.
+  static std::string GenerateSigninScopedDeviceID(bool for_ephemeral);
+
   // SigninClient implementation.
   PrefService* GetPrefs() override;
   scoped_refptr<TokenWebData> GetDatabase() override;