New post-sideload UI:

chrome/browser/extensions/extension_browsertest.h

Index: chrome/browser/extensions/extension_browsertest.h
diff --git a/chrome/browser/extensions/extension_browsertest.h b/chrome/browser/extensions/extension_browsertest.h
index aef8c36ab264057e59591d3ade0afc44587dcfea..88de75e048a179d368c0bc2f0ddde49262e24be5 100644
--- a/chrome/browser/extensions/extension_browsertest.h
+++ b/chrome/browser/extensions/extension_browsertest.h
@@ -14,6 +14,7 @@
 #include "chrome/browser/extensions/extension_host.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/features/feature.h"
+#include "chrome/common/extensions/feature_switch.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_observer.h"
@@ -249,6 +250,9 @@ class ExtensionBrowserTest : virtual public InProcessBrowserTest,
 
   // Make the current channel "dev" for the duration of the test.
   extensions::Feature::ScopedCurrentChannel current_channel_;
+
+  // Disable external install UI.
+  extensions::FeatureSwitch::ScopedOverride override_external_extension_prompt_;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_BROWSERTEST_H_