tracing: split trace event filter classes out of TraceLog

base/trace_event/event_name_filter.h

+// 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 BASE_TRACE_EVENT_EVENT_NAME_FILTER_H_
+#define BASE_TRACE_EVENT_EVENT_NAME_FILTER_H_
+
+#include <memory>
+#include <string>
+#include <unordered_set>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/trace_event/trace_event_filter.h"
+
+namespace base {
+namespace trace_event {
+
+class TraceEvent;
+
+// Filters trace events by checking the full name against a whitelist.
+// The current implementation is quite simple and dumb and just uses a
+// hashtable which requires char* to std::string conversion. It could be smarter
+// and use a bloom filter trie. However, today this is used too rarely to
+// justify that cost.
+class BASE_EXPORT EventNameFilter : public TraceEventFilter {
+ public:
+  using EventNamesWhitelist = std::unordered_set<std::string>;
+  static const char kName[];
+
+  EventNameFilter(std::unique_ptr<EventNamesWhitelist>);
+  ~EventNameFilter() override;
+
+  // TraceEventFilter implementation.
+  bool FilterTraceEvent(const TraceEvent&) const override;
+
+ private:
+  std::unique_ptr<const EventNamesWhitelist> event_names_whitelist_;
+
+  DISALLOW_COPY_AND_ASSIGN(EventNameFilter);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_EVENT_NAME_FILTER_H_