[subresource_filter] Add observer interface for page activation

components/subresource_filter/content/browser/subresource_filter_observer.h

Index: components/subresource_filter/content/browser/subresource_filter_observer.h
diff --git a/components/subresource_filter/content/browser/subresource_filter_observer.h b/components/subresource_filter/content/browser/subresource_filter_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..7daa78a65f738e5091ba17188001a11bbfaa9e77
--- /dev/null
+++ b/components/subresource_filter/content/browser/subresource_filter_observer.h
@@ -0,0 +1,34 @@
+// Copyright 2017 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_CONTENT_BROWSER_SUBRESOURCE_FILTER_OBSERVER_H_
+#define COMPONENTS_SUBRESOURCE_FILTER_CONTENT_BROWSER_SUBRESOURCE_FILTER_OBSERVER_H_
+
+#include "components/subresource_filter/core/common/activation_decision.h"
+
+namespace content {
+class NavigationHandle;
+}  // namespace content
+
+namespace subresource_filter {
+
+struct ActivationState;
+
+// Class to receive notifications of subresource filter events for a given
+// WebContents. Registered with a SubresourceFilterObserverManager.
+class SubresourceFilterObserver {
+ public:
+  virtual ~SubresourceFilterObserver() = default;
+
+  virtual void OnSubresourceFilterGoingAway() {}
+
+  virtual void OnPageActivationComputed(
+      content::NavigationHandle* navigation_handle,
+      ActivationDecision activation_decision,
+      const ActivationState& activation_state) {}
+};
+
+}  // namespace subresource_filter
+
+#endif  // COMPONENTS_SUBRESOURCE_FILTER_CONTENT_BROWSER_SUBRESOURCE_FILTER_OBSERVER_H_