[on-hold][subresource_filter] Add ActivationTracker to track all activated contents

chrome/browser/subresource_filter/subresource_filter_activation_tracker.h

+// 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 CHROME_BROWSER_SUBRESOURCE_FILTER_SUBRESOURCE_FILTER_ACTIVATION_TRACKER_H_
+#define CHROME_BROWSER_SUBRESOURCE_FILTER_SUBRESOURCE_FILTER_ACTIVATION_TRACKER_H_
+
+#include <set>
+
+#include "base/macros.h"
+
+namespace content {
+class WebContents;
+}  // namespace content
+
+class SubresourceFilterActivationTracker {
+ public:
+  SubresourceFilterActivationTracker();
+  ~SubresourceFilterActivationTracker();
+
+  void OnWebContentsActivated(content::WebContents* web_contents,
+                              bool activated);
+  void OnWebContentsDestroyed(content::WebContents* web_contents);
+
+  bool HasActivatedWebContents() const;
+
+ private:
+  std::set<content::WebContents*> activated_contents_;
+  DISALLOW_COPY_AND_ASSIGN(SubresourceFilterActivationTracker);
+};
+
+#endif  // CHROME_BROWSER_SUBRESOURCE_FILTER_SUBRESOURCE_FILTER_ACTIVATION_TRACKER_H_