Put extension enable logic into a ExtensionEnableFlow.

chrome/browser/ui/extensions/extension_enable_flow_delegate.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_EXTENSIONS_EXTENSION_ENABLE_FLOW_DELEGATE_H_
+#define CHROME_BROWSER_UI_EXTENSIONS_EXTENSION_ENABLE_FLOW_DELEGATE_H_
+
+class ExtensionInstallPrompt;
+class ExtensionEnableFlow;
+
+class ExtensionEnableFlowDelegate {
+ public:
+  // Invoked to create an ExtensionInstallPrompt for the flow to use. Caller
+  // takes ownership of the return ExtensionInstallPrompt;
+  virtual ExtensionInstallPrompt* CreateExtensionInstallPrompt() = 0;
+
+  // Invoked when |flow| is finished successfully.
+  virtual void ExtensionEnableFlowFinished(ExtensionEnableFlow* flow) = 0;
+
+  // Invoked when |flow| is aborted.
+  virtual void ExtensionEnableFlowAborted(ExtensionEnableFlow* flow,

[benwells, 2013/01/03 00:30:17]

Why pass the flow back? I can see this would enable multiple flows to happen
concurrently, is that something the other launcher / app list will use?

[xiyuan, 2013/01/07 18:13:12]

Agreed. We should not encourage concurrent usage of it.

+                                          bool user_initiated) = 0;
+
+ protected:
+  virtual ~ExtensionEnableFlowDelegate() {}
+};
+
+#endif  // CHROME_BROWSER_UI_EXTENSIONS_EXTENSION_ENABLE_FLOW_DELEGATE_H_