[subresource_filter] Add debugging trace events around activation

components/subresource_filter/core/browser/subresource_filter_features_test_support.h

 // 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.
 
 #ifndef COMPONENTS_SUBRESOURCE_FILTER_CORE_BROWSER_SUBRESOURCE_FILTER_FEATURES_TEST_SUPPORT_H_
 #define COMPONENTS_SUBRESOURCE_FILTER_CORE_BROWSER_SUBRESOURCE_FILTER_FEATURES_TEST_SUPPORT_H_
 
+#include <iosfwd>
 #include <memory>
 #include <string>
 
 #include "base/feature_list.h"
 #include "base/macros.h"
 #include "base/test/scoped_feature_list.h"
 #include "components/subresource_filter/core/browser/subresource_filter_features.h"
 
 namespace subresource_filter {
 namespace testing {
@@ skipping 44 matching lines @@
       base::FeatureList::OverrideState feature_state,
       const std::string& additional_features_to_enable = std::string());
 
  private:
   ScopedSubresourceFilterConfigurator scoped_configuration_;
   std::unique_ptr<base::test::ScopedFeatureList> scoped_feature_list_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedSubresourceFilterFeatureToggle);
 };
 
+// For logging in tests.
+std::ostream& operator<<(std::ostream& os, const Configuration& config);
+
 }  // namespace testing
 }  // namespace subresource_filter
 
 #endif  // COMPONENTS_SUBRESOURCE_FILTER_CORE_BROWSER_SUBRESOURCE_FILTER_FEATURES_TEST_SUPPORT_H_