Add an experiment for the default browser infobar on Windows 10

chrome/browser/shell_integration.h

Index: chrome/browser/shell_integration.h
diff --git a/chrome/browser/shell_integration.h b/chrome/browser/shell_integration.h
index d4d22383346f477318218f44db3d9280a350130b..7730a029341a1784afa657930d611138218a5a36 100644
--- a/chrome/browser/shell_integration.h
+++ b/chrome/browser/shell_integration.h
@@ -213,9 +213,10 @@ class DefaultBrowserWorker : public DefaultWebClientWorker {
  public:
   explicit DefaultBrowserWorker(const DefaultWebClientWorkerCallback& callback);
 
- private:
+ protected:
   ~DefaultBrowserWorker() override;
 
+ private:
   // Check if Chrome is the default browser.
   DefaultWebClientState CheckIsDefaultImpl() override;