[Extensions] Migrate ExtensionInstallPrompt::Delegate to be a callback

chrome/browser/extensions/webstore_standalone_installer.h

Index: chrome/browser/extensions/webstore_standalone_installer.h
diff --git a/chrome/browser/extensions/webstore_standalone_installer.h b/chrome/browser/extensions/webstore_standalone_installer.h
index 70151fa7de3f69ca596b395459e90212e19a7b21..5cb43a269a45cd82722e4ef7f0467c1f2b3b80de 100644
--- a/chrome/browser/extensions/webstore_standalone_installer.h
+++ b/chrome/browser/extensions/webstore_standalone_installer.h
@@ -45,7 +45,6 @@ class WebstoreDataFetcher;
 
 class WebstoreStandaloneInstaller
     : public base::RefCountedThreadSafe<WebstoreStandaloneInstaller>,
-      public ExtensionInstallPrompt::Delegate,
       public WebstoreDataFetcherDelegate,
       public WebstoreInstaller::Delegate,
       public WebstoreInstallHelper::Delegate {
@@ -152,9 +151,8 @@ class WebstoreStandaloneInstaller
   // Create an approval to pass installation parameters to the CrxInstaller.
   virtual scoped_ptr<WebstoreInstaller::Approval> CreateApproval() const;
 
-  // ExtensionInstallPrompt::Delegate interface implementation.
-  void InstallUIProceed() override;
-  void InstallUIAbort(bool user_initiated) override;
+  // Called once the install prompt has finished.
+  virtual void OnInstallPromptDone(ExtensionInstallPrompt::Result result);
 
   // Accessors to be used by subclasses.
   bool show_user_count() const { return show_user_count_; }