Use an infobar instead of alert box for extension install error.

chrome/browser/extensions/crx_installer_error.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_EXTENSIONS_CRX_INSTALLER_ERROR_H_
+#define CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_ERROR_H_
+#pragma once
+
+#include "base/string16.h"
+
+// Simple error class for CrxInstaller.
+class CrxInstallerError {
+ public:
+  // Typed errors that need to be handled specially by clients.
+  enum Type {
+    ERROR_NONE,
+    ERROR_OFF_STORE,
+    ERROR_OTHER
+  };
+
+  CrxInstallerError() : type_(ERROR_NONE) {
+  }
+
+  explicit CrxInstallerError(const string16& message)
+      : type_(message.empty() ? ERROR_NONE : ERROR_OTHER),
+        message_(message) {
+  }
+
+  CrxInstallerError(Type type, const string16& message)
+      : type_(type), message_(message) {
+  }
+
+  Type type() const { return type_; }
+  const string16& message() const { return message_; }
+
+ private:
+  Type type_;
+  string16 message_;
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_ERROR_H_