Add a group policy controlling which sites can install extensions.

chrome/browser/extensions/crx_installer.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_H_
 #define CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_
 #pragma once
 
 #include <string>
 
@@ skipping 36 matching lines @@
 // working with it, eg:
 //
 // scoped_refptr<CrxInstaller> installer(new CrxInstaller(...));
 // installer->set_foo();
 // installer->set_bar();
 // installer->InstallCrx(...);
 class CrxInstaller
     : public SandboxedExtensionUnpackerClient,
       public ExtensionInstallUI::Delegate {
  public:
+  // Used in histograms; do not change order.
+  enum OffStoreInstallAllowReason {
+    OffStoreInstallDisallowed,
+    OffStoreInstallAllowedFromSettingsPage,
+    OffStoreInstallAllowedBecausePref,

[Mattias Nissler (ping if slow), 2012/06/08 09:38:22]

nit: I'd rename this to OffStoreInstallAllowedByPref, up to you.

+    OffStoreInstallAllowedInTest,
+    NumOffStoreInstallAllowReasons

[Mattias Nissler (ping if slow), 2012/06/08 09:38:22]

Style guide says "Though the Google C++ Style Guide says to use kConstantNaming
for enums, Chrome still uses MACRO_STYLE naming for enums for consistency with
our existing code.". These enum constants don't follow either style.

+  };
+
   // Extensions will be installed into frontend->install_directory(),
   // then registered with |frontend|. Any install UI will be displayed
   // using |client|. Pass NULL for |client| for silent install
   static scoped_refptr<CrxInstaller> Create(
       ExtensionService* frontend,
       ExtensionInstallUI* client);
 
   // Same as the previous method, except use the |approval| to bypass the
   // prompt. Note that the caller retains ownership of |approval|.
   static scoped_refptr<CrxInstaller> Create(
@@ skipping 72 matching lines @@
     original_mime_type_ = original_mime_type;
   }
 
   extension_misc::CrxInstallCause install_cause() const {
     return install_cause_;
   }
   void set_install_cause(extension_misc::CrxInstallCause install_cause) {
     install_cause_ = install_cause;
   }
 
-  bool allow_off_store_install() const { return allow_off_store_install_; }
-  void set_allow_off_store_install(bool val) { allow_off_store_install_ = val; }
+  OffStoreInstallAllowReason off_store_install_allow_reason() const {
+    return off_store_install_allow_reason_;
+  }
+  void set_off_store_install_allow_reason(OffStoreInstallAllowReason reason) {
+    off_store_install_allow_reason_ = reason;
+  }
 
   void set_page_ordinal(const StringOrdinal& page_ordinal) {
     page_ordinal_ = page_ordinal;
   }
 
   Profile* profile() { return profile_; }
 
  private:
   friend class extensions::ExtensionUpdaterTest;
 
@@ skipping 144 matching lines @@
 
   // What caused this install?  Used only for histograms that report
   // on failure rates, broken down by the cause of the install.
   extension_misc::CrxInstallCause install_cause_;
 
   // Creation flags to use for the extension.  These flags will be used
   // when calling Extenion::Create() by the crx installer.
   int creation_flags_;
 
   // Whether to allow off store installation.
-  bool allow_off_store_install_;
+  OffStoreInstallAllowReason off_store_install_allow_reason_;
 
   DISALLOW_COPY_AND_ASSIGN(CrxInstaller);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_