extensions: Abstract out install delay strategy

chrome/browser/extensions/update_install_gate.h

+// Copyright 2016 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_EXTENSIONS_UPDATE_INSTALL_GATE_H_
+#define CHROME_BROWSER_EXTENSIONS_UPDATE_INSTALL_GATE_H_
+
+#include "base/macros.h"
+#include "chrome/browser/extensions/install_gate.h"
+
+class ExtensionService;
+
+namespace extensions {
+
+// Delays an extension update if the old version is not idle.
+class UpdateInstallGate : public InstallGate {
+ public:
+  explicit UpdateInstallGate(ExtensionService* service);
+
+  // InstallGate:
+  Action ShouldDelay(const Extension* extension,
+                     bool install_immediately) override;
+
+ private:
+  // Not owned.
+  ExtensionService* const service_;
+
+  DISALLOW_COPY_AND_ASSIGN(UpdateInstallGate);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_UPDATE_INSTALL_GATE_H_