Move Extension Location and Type enums to Manifest, and move InstallWarning to its own file.

extensions/common/install_warning.h

+// Copyright (c) 2013 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 EXTENSIONS_COMMON_INSTALL_WARNING_H_
+#define EXTENSIONS_COMMON_INSTALL_WARNING_H_
+
+#include <ostream>
+#include <string>
+
+namespace extensions {
+
+struct InstallWarning {
+  enum Format {
+    // IMPORTANT: Do not build HTML strings from user or developer-supplied
+    // input.
+    FORMAT_TEXT,
+    FORMAT_HTML,
+  };
+  InstallWarning(Format format, const std::string& message)
+      : format(format), message(message) {
+  }
+  bool operator==(const InstallWarning& other) const {
+    return format == other.format && message == other.message;
+  }
+  Format format;
+  std::string message;
+};
+
+// Let gtest print InstallWarnings.
+void PrintTo(const InstallWarning&, ::std::ostream* os);
+
+}  // namespace
+
+#endif  // EXTENSIONS_COMMON_INSTALL_WARNING_H_