Adding client code for new desktop First Run Experience.

chrome/common/url_constants.h

Index: chrome/common/url_constants.h
diff --git a/chrome/common/url_constants.h b/chrome/common/url_constants.h
index cafdbbd797b4ca3ece9dd3ee8cb57438ef0dbf70..8ceaa4ccf7d4ae2298f9340fe45fe93d9e2317d0 100644
--- a/chrome/common/url_constants.h
+++ b/chrome/common/url_constants.h
@@ -86,6 +86,7 @@ extern const char kChromeUIUberFrameURL[];
 extern const char kChromeUIUserActionsURL[];
 extern const char kChromeUIUserManagerURL[];
 extern const char kChromeUIVersionURL[];
+extern const char kChromeUIWelcomeURL[];
 
 #if BUILDFLAG(ANDROID_JAVA_UI)
 extern const char kChromeUIContextualSearchPromoURL[];
@@ -236,6 +237,7 @@ extern const char kChromeUIUberHost[];
 extern const char kChromeUIUsbInternalsHost[];
 extern const char kChromeUIUserActionsHost[];
 extern const char kChromeUIVersionHost[];
+extern const char kChromeUIWelcomeHost[];
 extern const char kChromeUIWorkersHost[];
 
 extern const char kChromeUIThemePath[];