PreloadCheck class for extension pre-install checks

extensions/browser/preload_check.h

Index: extensions/browser/preload_check.h
diff --git a/extensions/browser/preload_check.h b/extensions/browser/preload_check.h
new file mode 100644
index 0000000000000000000000000000000000000000..011cbbbb2952eb7818f69b3da0a66bd1797088c6
--- /dev/null
+++ b/extensions/browser/preload_check.h
@@ -0,0 +1,60 @@
+// Copyright 2017 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_BROWSER_PRELOAD_CHECK_H_
+#define EXTENSIONS_BROWSER_PRELOAD_CHECK_H_
+
+#include <memory>
+#include <unordered_set>
+#include <utility>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/strings/string16.h"
+#include "extensions/common/extension.h"
+
+namespace extensions {
+
+// Encapsulates a possibly asynchronous operation to verify whether a
+// precondition holds for loading the given extension.
+class PreloadCheck {
+ public:
+  // These enumerators should only be referred to by name, so it is safe to
+  // insert or remove values as necessary.
+  enum Error {
+    NONE,
+    BLACKLISTED_ID,
+    BLACKLISTED_UNKNOWN,
+    DISALLOWED_BY_POLICY,
+  };
+
+  // TODO(michaelpg): Remove std::hash<int> template argument once std::hash
+  // directly supports enums.
+  // See http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2148
+  using Errors = std::unordered_set<Error, std::hash<int>>;

[Devlin, 2017/03/14 01:44:34]

Any reason to use unordered_set here?  Seems like for the number of errors we'd
get, either std::set<> (for its canonicalism) or base::flat_set (for its
speed/optimization) would be more appropriate.

[michaelpg, 2017/03/14 21:58:30]

/shrug/ std::set sgtm

+  using ResultCallback = base::OnceCallback<void(Errors)>;
+
+  explicit PreloadCheck(scoped_refptr<const Extension> extension);
+  virtual ~PreloadCheck();
+
+  // This function must be called on the UI thread. The callback also occurs on
+  // the UI thread.
+  virtual void Start(ResultCallback callback) = 0;
+
+  // Subclasses may provide an error message.
+  virtual base::string16 GetErrorMessage() const;
+
+  const Extension* extension() { return extension_.get(); }
+
+ private:
+  // The extension to check.
+  scoped_refptr<const Extension> extension_;
+
+  DISALLOW_COPY_AND_ASSIGN(PreloadCheck);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_PRELOAD_CHECK_H_