Split a MetricsLogStore object out of MetricsLogManager.

components/metrics/log_store.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 COMPONENTS_METRICS_LOG_STORE_H_
+#define COMPONENTS_METRICS_LOG_STORE_H_
+
+#include <string>
+
+namespace metrics {
+
+// Interface for local storage of logs to be reported.

[rkaplow, 2017/02/20 21:24:13]

nit, since you're organizing this into an interface, might be worth adding a
couple lines of explaination on how this can get used, i.e. what features are
available

[Steven Holte, 2017/02/21 21:51:18]

Done.

+class LogStore {
+ public:
+  // Returns true if there are any logs waiting to be uploaded.
+  virtual bool has_unsent_logs() const = 0;
+
+  // Returns true if there is a log that needs to be, or is being, uploaded.
+  virtual bool has_staged_log() const = 0;
+
+  // The text of the staged log, as a serialized protobuf.
+  // Will trigger a DCHECK if there is no staged log.
+  virtual const std::string& staged_log() const = 0;
+
+  // The SHA1 hash of the staged log.
+  // Will trigger a DCHECK if there is no staged log.
+  virtual const std::string& staged_log_hash() const = 0;
+
+  // Populates staged_log() with the next stored log to send.
+  // The staged_log will remain the same even if additional logs are added.

[rkaplow, 2017/02/20 21:24:13]

can you define a bit more what 'next' means in this context

[Steven Holte, 2017/02/21 21:51:18]

Added a comment saying this is explicitly left to the implementation.

+  // Should only be called if has_unsent_logs() is true.
+  virtual void StageNextLog() = 0;
+
+  // Discards the staged log.
+  virtual void DiscardStagedLog() = 0;
+
+  // Saves any unsent logs to persistent storage.
+  virtual void PersistUnsentLogs() const = 0;
+
+  // Loads unsent logs from persistent storage.
+  virtual void LoadPersistedUnsentLogs() = 0;
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_LOG_STORE_H_