tracing: split trace event filter classes out of TraceLog

base/trace_event/heap_profiler_event_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_HEAP_PROFILER_EVENT_FILTER_H_
+#define BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_FILTER_H_
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/trace_event/trace_event_filter.h"
+
+namespace base {
+namespace trace_event {
+
+class TraceEvent;
+
+// This filter unconditionally accepts all events and pushes/pops them from the
+// thread-local AllocationContextTracker instance as they are seen.
+// This is used to cheaply construct the heap profiler pseudo stack without
+// having to actually record all events.
+class BASE_EXPORT HeapProfilerEventFilter : public TraceEventFilter {
+ public:
+  static const char kName[];
+
+  HeapProfilerEventFilter();
+  ~HeapProfilerEventFilter() override;
+
+  // TraceEventFilter implementation.
+  bool FilterTraceEvent(const TraceEvent& trace_event) const override;
+  void EndEvent(const char* category_name,
+                const char* event_name) const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(HeapProfilerEventFilter);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_FILTER_H_