Introduce subresource_filter::ConfigurationList and make querying it cheap.

components/subresource_filter/core/browser/subresource_filter_features_test_support.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 "components/subresource_filter/core/browser/subresource_filter_features_test_support.h"
 
 #include <map>
 #include <memory>
 
 #include "base/metrics/field_trial.h"
@@ skipping 47 matching lines @@
   if (existing_feature_list) {
     std::string enabled_features;
     std::string disabled_features;
     base::FeatureList::GetInstance()->GetFeatureOverrides(&enabled_features,
                                                           &disabled_features);
     feature_list->InitializeFromCommandLine(enabled_features,
                                             disabled_features);
   }
 
   scoped_feature_list_.InitWithFeatureList(std::move(feature_list));
+
+  // Force the active ConfigurationList to be reparsed on next access so that
+  // the variation parameters come into effect.
+  ClearCachedActiveConfigurations();
 }
 
 ScopedSubresourceFilterFeatureToggle::~ScopedSubresourceFilterFeatureToggle() {
   variations::testing::ClearAllVariationParams();
+
+  // Force the active ConfigurationList to be reparsed on next access, so that
+  // the overrides from this instance are no longer in effect.
+  ClearCachedActiveConfigurations();
 }
 
 }  // namespace testing
 }  // namespace subresource_filter