Introduce subresource_filter::ConfigurationList and make querying it cheap.

chrome/browser/component_updater/subresource_filter_component_installer.cc

 // Copyright 2016 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.
 
 #include "chrome/browser/component_updater/subresource_filter_component_installer.h"
 
 #include <utility>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
@@ skipping 94 matching lines @@
     std::vector<uint8_t>* hash) const {
   hash->assign(std::begin(kPublicKeySHA256), std::end(kPublicKeySHA256));
 }
 
 std::string SubresourceFilterComponentInstallerTraits::GetName() const {
   return kSubresourceFilterSetFetcherManifestName;
 }
 
 // static
 std::string SubresourceFilterComponentInstallerTraits::GetInstallerTag() {
-  std::string ruleset_flavor =
-      subresource_filter::GetActiveConfiguration().ruleset_flavor;
+  std::string ruleset_flavor = subresource_filter::GetActiveConfigurations()

[Sorin Jianu, 2017/04/24 21:58:59]

can this be declared const?

[engedy, 2017/04/25 08:34:23]

Yep, done.

+                                   ->the_one_and_only()
+                                   .ruleset_flavor;
   if (ruleset_flavor.empty())
     return ruleset_flavor;
 
   // We allow 4 ruleset flavor identifiers: a, b, c, d
   if (ruleset_flavor.size() == 1 && ruleset_flavor.at(0) >= 'a' &&
       ruleset_flavor.at(0) <= 'd')
     return ruleset_flavor;
 
   // Return 'invalid' for any cases where we encounter an invalid installer
   // tag. This allows us to verify that no clients are encountering invalid
@@ skipping 21 matching lines @@
     return;
   std::unique_ptr<ComponentInstallerTraits> traits(
       new SubresourceFilterComponentInstallerTraits());
   // |cus| will take ownership of |installer| during installer->Register(cus).
   DefaultComponentInstaller* installer =
       new DefaultComponentInstaller(std::move(traits));
   installer->Register(cus, base::Closure());
 }
 
 }  // namespace component_updater