Introduce activation scope logic.

components/subresource_filter/core/common/activation_scope.h

Index: components/subresource_filter/core/common/activation_scope.h
diff --git a/components/subresource_filter/core/common/activation_scope.h b/components/subresource_filter/core/common/activation_scope.h
new file mode 100644
index 0000000000000000000000000000000000000000..699f3caa474388b72e7a7b9842fc5855b96d1f2d
--- /dev/null
+++ b/components/subresource_filter/core/common/activation_scope.h
@@ -0,0 +1,25 @@
+// 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_COMMON_ACTIVATION_SCOPE_H_
+#define COMPONENTS_SUBRESOURCE_FILTER_CORE_COMMON_ACTIVATION_SCOPE_H_
+
+#include <iosfwd>
+
+namespace subresource_filter {
+
+// Defines the scope of triggering the Safe Browsing Subresource Filter.
+enum class ActivationScope {
+  DISABLED,

[engedy, 2016/08/04 13:26:54]

`Disabled` sounds strange for a `scope`. What do you think about NOWHERE or
NO_SITES?

+  ALL_SITES,

[engedy, 2016/08/04 13:26:54]

nit: Could you please document what ALL_SITES and ACTIVATION_LIST means? For
ALL_SITES, also mention that it is used for testing.

[engedy, 2016/08/04 13:26:55]

Let's flip line 15 and 16 so the enumerators are in order of increasing extent.

[melandory, 2016/08/04 14:06:41]

Done.

[melandory, 2016/08/04 14:06:41]

Done.

+  ACTIVATION_LIST,
+  LAST = ACTIVATION_LIST,
+};
+
+// For logging use only.
+std::ostream& operator<<(std::ostream& os, const ActivationScope& state);
+
+}  // namespace subresource_filter
+
+#endif  // COMPONENTS_SUBRESOURCE_FILTER_CORE_COMMON_ACTIVATION_SCOPE_H_