[UMA] Use proper C++ objects to serialize tracked_objects across process boundaries.

chrome/browser/metrics/tracking_synchronizer_observer.h

+// Copyright (c) 2012 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_METRICS_TRACKING_SYNCHRONIZER_OBSERVER_H_
+#define CHROME_BROWSER_METRICS_TRACKING_SYNCHRONIZER_OBSERVER_H_
+#pragma once
+
+namespace content {
+struct SerializedProfilerData;
+}
+
+namespace chrome_browser_metrics {
+
+// Observer for notifications from the TrackingSynchronizer class.
+class TrackingSynchronizerObserver {
+ public:
+  // Received profiler |data| from a single process.  The observer should assume
+  // there might be more data coming until |FinishedReceivingData()| is called.
+  virtual void ReceivedProfilerData(
+      const content::SerializedProfilerData& data) = 0;
+
+  // The observer should not expect any more calls to |ReceivedProfilerData()|
+  // (without re-registering).  This is sent either when data from all processes
+  // has been gathered, or when the request times out.
+  virtual void FinishedReceivingProfilerData() {}
+
+ protected:
+  TrackingSynchronizerObserver() {}
+  virtual ~TrackingSynchronizerObserver() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TrackingSynchronizerObserver);
+};
+
+}  // namespace chrome_browser_metrics
+
+#endif  // CHROME_BROWSER_METRICS_TRACKING_SYNCHRONIZER_OBSERVER_H_