Bound the impact of system instability on chrome instability.

components/browser_watcher/system_session_analyzer_win.h

Index: components/browser_watcher/system_session_analyzer_win.h
diff --git a/components/browser_watcher/system_session_analyzer_win.h b/components/browser_watcher/system_session_analyzer_win.h
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+// 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_BROWSER_WATCHER_SYSTEM_SESSION_ANALYZER_WIN_H_
+#define COMPONENTS_BROWSER_WATCHER_SYSTEM_SESSION_ANALYZER_WIN_H_
+
+#include <map>
+#include <memory>
+#include <vector>
+
+#include "base/gtest_prod_util.h"
+#include "base/time/time.h"
+
+namespace browser_watcher {
+
+// Analyzes system session events for unclean sessions. Initialization is
+// expensive and therefore done lazily, as the analyzer is instantiated before
+// knowing whether it will be used.
+class SystemSessionAnalyzer {
+ public:
+  enum Status {
+    FAILED = 0,
+    CLEAN = 1,
+    UNCLEAN = 2,
+    OUTSIDE_RANGE = 3,
+  };
+
+  // Minimal information about a log event.
+  struct EventInfo {
+    uint16_t event_id;
+    base::Time event_time;
+  };
+
+  // Creates a SystemSessionAnalyzer that will analyze system sessions based on
+  // events pertaining to the last session_cnt system sessions.
+  explicit SystemSessionAnalyzer(uint32_t session_cnt);
+  virtual ~SystemSessionAnalyzer();
+
+  // Returns an analysis status for the system session that contains timestamp.
+  virtual Status IsSessionUnclean(base::Time timestamp);
+
+ protected:
+  // Queries for events pertaining to the last session_cnt sessions. On success,
+  // returns true and event_infos contains events ordered from newest to oldest.
+  // Returns false otherwise. Virtual for unit testing.
+  virtual bool FetchEvents(std::vector<EventInfo>* event_infos) const;
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(SystemSessionAnalyzerTest, FetchEvents);
+
+  bool Initialize();
+
+  // The number of sessions to query events for.
+  uint32_t session_cnt_;
+
+  bool initialized_ = false;
+  bool init_success_ = false;
+
+  // Information about unclean sessions: start time to duration until the next
+  // session start, ie *not* session duration. Note: it's easier to get the
+  // delta to the next session start, and changes nothing wrt classifying
+  // events that occur during sessions assuming query timestamps fall within
+  // system sessions.
+  std::map<base::Time, base::TimeDelta> unclean_sessions_;
+
+  // Timestamp of the oldest event.
+  base::Time coverage_start_;
+
+  DISALLOW_COPY_AND_ASSIGN(SystemSessionAnalyzer);
+};
+
+}  // namespace browser_watcher
+
+#endif  // COMPONENTS_BROWSER_WATCHER_SYSTEM_SESSION_ANALYZER_WIN_H_