Refactor the various ways to control what users can do to extensions.

chrome/browser/extensions/management_policy.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_MANAGEMENT_POLICY_H_
+#define CHROME_BROWSER_EXTENSIONS_MANAGEMENT_POLICY_H_
+#pragma once
+
+#include <set>
+#include <string>
+
+#include "base/basictypes.h"
+#include "chrome/common/extensions/extension.h"
+
+namespace extensions {
+
+// This class registers providers that want to prohibit certain actions from
+// being applied to extensions. It must be called, via the ExtensionService,
+// before allowing a user or a user-level mechanism to perform the respective
+// action. (That is, installing or otherwise modifying an extension in order
+// to conform to enterprise administrator policy must be exempted from these
+// checks.)
+//
+// This "policy" and its providers should not be confused with administrator
+// policy, although admin policy is one of the sources ("Providers") of
+// restrictions registered with and exposed by the ManagementPolicy.
+class ManagementPolicy {
+ public:
+  // Each mechanism that wishes to limit users' ability to control extensions,
+  // whether one individual extension or the whole system, should implement
+  // the methods of this Provider interface that it needs. In each case, if the
+  // provider does not need to control a certain action, that method does not
+  // need to be implemented.
+  //
+  // It is not guaranteed that a particular Provider's methods will be called
+  // each time a user tries to perform one of the controlled actions (the list
+  // of providers is short-circuited as soon as a decision is possible), so
+  // implementations of these methods must have no side effects.
+  //
+  // For all of the Provider methods below, if |error| is not NULL and the
+  // method imposes a restriction on the desired action, |error| may be set
+  // to an applicable error message, but this is not required.
+  class Provider {
+   public:
+    Provider() {}
+    virtual ~Provider() {}
+
+    // A human-readable name for this provider, for use in debug messages.
+    virtual std::string GetPolicyProviderName() const = 0;
+
+    // Providers should return false if a user may not install the |extension|,
+    // or load or run it if it has already been installed.
+    virtual bool UserMayLoad(const Extension* extension,
+                             string16* error) const;
+
+    // Providers should return false if a user may not enable, disable, or
+    // uninstall the |extension|, or change its usage options (incognito
+    // permission, file access, etc.).
+    virtual bool UserMayModifySettings(const Extension* extension,
+                                       string16* error) const;
+
+    // Providers should return true if the |extension| must always remain
+    // enabled. This is distinct from UserMayModifySettings() in that the latter
+    // also prohibits enabling the extension if it is currently disabled.
+    // Providers implementing this method should also implement the others
+    // above, if they wish to completely lock in an extension.
+    virtual bool MustRemainEnabled(const Extension* extension,
+                                   string16* error) const;
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(Provider);
+  };
+
+  ManagementPolicy();
+  ~ManagementPolicy();
+
+  // Registers or unregisters a provider, causing it to be added to or removed
+  // from the list of providers queried. Ownership of the provider remains with
+  // the caller. Providers do not need to be unregistered on shutdown.
+  void RegisterProvider(Provider* provider);
+  void UnregisterProvider(Provider* provider);
+
+  // Returns true if the user is permitted to install, load, and run the given
+  // extension. If not, |error| may be set to an appropriate message.
+  bool UserMayLoad(const Extension* extension, string16* error) const;
+
+  // Returns true if the user is permitted to enable, disable, or uninstall the
+  // given extension, or change the extension's usage options (incognito mode,
+  // file access, etc.). If not, |error| may be set to an appropriate message.
+  bool UserMayModifySettings(const Extension* extension,
+                             string16* error) const;
+
+  // Returns true if the extension must remain enabled at all times (e.g. a
+  // compoment extension). In that case, |error| may be set to an appropriate
+  // message.
+  bool MustRemainEnabled(const Extension* extension,
+                         string16* error) const;
+
+  // For use in testing.
+  void UnregisterAllProviders();
+  int GetNumProviders() const;
+
+ private:
+  typedef std::set<Provider*> ProviderList;
+  ProviderList providers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ManagementPolicy);
+};
+
+}  // namespace
+
+#endif  // CHROME_BROWSER_EXTENSIONS_MANAGEMENT_POLICY_H_