memory-infra: Start disentangling tracing from memory-infra

base/trace_event/memory_tracing_observer.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 BASE_TRACE_EVENT_MEMORY_TRACING_OBSERVER_H_
+#define BASE_TRACE_EVENT_MEMORY_TRACING_OBSERVER_H_
+
+#include "base/macros.h"
+#include "base/trace_event/memory_dump_manager.h"
+#include "base/trace_event/trace_event.h"
+
+namespace base {
+
+namespace trace_event {
+
+// Observes TraceLog for Enable/Disable events and when they occur Enables and
+// Disables the MemoryDumpManager with the correct state based on reading the
+// trace log. Also provides a method for adding a dump to the trace.
+class BASE_EXPORT MemoryTracingObserver
+    : public TraceLog::EnabledStateObserver {
+ public:
+  static const char* const kTraceCategory;
+
+  MemoryTracingObserver(TraceLog*, MemoryDumpManager*);
+  ~MemoryTracingObserver() override;
+
+  // TraceLog::EnabledStateObserver implementation.
+  void OnTraceLogEnabled() override;
+  void OnTraceLogDisabled() override;
+
+  bool AddDumpToTraceIfEnabled(const MemoryDumpRequestArgs*,
+                               const ProcessId,
+                               const ProcessMemoryDump*);
+
+ private:
+  MemoryDumpManager* const memory_dump_manager_;
+  TraceLog* const trace_log_;
+
+  DISALLOW_COPY_AND_ASSIGN(MemoryTracingObserver);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_MEMORY_TRACING_OBSERVER_H_