Introduce activation scope logic.

components/subresource_filter/core/browser/subresource_filter_features.h

Index: components/subresource_filter/core/browser/subresource_filter_features.h
diff --git a/components/subresource_filter/core/browser/subresource_filter_features.h b/components/subresource_filter/core/browser/subresource_filter_features.h
index 612a2d9f1d6956d56b0dd45c5c63d56c826d9ac1..0d972a7f30d25b8da35f6e138645afe6f8a111e6 100644
--- a/components/subresource_filter/core/browser/subresource_filter_features.h
+++ b/components/subresource_filter/core/browser/subresource_filter_features.h
@@ -6,6 +6,7 @@
 #define COMPONENTS_SUBRESOURCE_FILTER_SUBRESOURCE_FILTER_FEATURES_H_
 
 #include "base/feature_list.h"
+#include "components/subresource_filter/core/common/activation_scope.h"
 #include "components/subresource_filter/core/common/activation_state.h"
 
 namespace subresource_filter {
@@ -19,11 +20,22 @@ extern const char kActivationStateDryRun[];
 extern const char kActivationStateEnabled[];
 extern const char kActivationStateDisabled[];
 
+extern const char kActivationScopeParameterName[];
+extern const char kActivationScopeAllSites[];
+extern const char kActivationScopeActivationList[];
+extern const char kActivationScopeNoSites[];
+
 // Returns the maximum degree to which subresource filtering should be activated
 // on any RenderFrame. This will be ActivationState::DISABLED unless the feature
 // is enabled and variation parameters prescribe a higher activation state.
 ActivationState GetMaximumActivationState();
 
+// Returns the current activation scope, that is, the subset of page loads where
+// subresource filtering should be activated. The function returns
+// ActivationScope::NO_SITES unless the feature is enabled and variation
+// parameters prescribe a wider activation scope.
+ActivationScope GetCurrentActivationScope();
+
 }  // namespace subresource_filter
 
 #endif  // COMPONENTS_SUBRESOURCE_FILTER_SUBRESOURCE_FILTER_FEATURES_H_