sync: add InternalComponentsFactory::Switches to simplify passing switches to internal components.

sync/engine/backoff_delay_provider.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 SYNC_ENGINE_BACKOFF_DELAY_PROVIDER_H_
+#define SYNC_ENGINE_BACKOFF_DELAY_PROVIDER_H_
+
+#include "base/time.h"
+
+namespace syncer {
+
+namespace sessions {
+struct ModelNeutralState;
+}
+
+// A component used to get time delays associated with exponential backoff.
+class BackoffDelayProvider {
+ public:
+  // Factory function to create a standard BackoffDelayProvider.
+  static BackoffDelayProvider* FromDefaults();
+
+  // Similar to above, but causes sync to retry very quickly (see
+  // polling_constants.h) when it encounters an error before exponential
+  // backoff.
+  //
+  // *** NOTE *** This should only be used if kSyncShortInitialRetryOverride
+  // was passed to command line.
+  static BackoffDelayProvider* WithShortInitialRetryOverride();
+
+  virtual ~BackoffDelayProvider();
+
+  // DDOS avoidance function.  Calculates how long we should wait before trying
+  // again after a failed sync attempt, where the last delay was |base_delay|.
+  // TODO(tim): Look at URLRequestThrottlerEntryInterface.
+  virtual base::TimeDelta GetDelay(const base::TimeDelta& last_delay);
+
+  // Helper to calculate the initial value for exponential backoff.
+  // See possible values and comments in polling_constants.h.
+  virtual base::TimeDelta GetInitialDelay(
+      const sessions::ModelNeutralState& state) const;
+
+ protected:
+  BackoffDelayProvider(const base::TimeDelta& default_initial_backoff,
+                       const base::TimeDelta& short_initial_backoff);
+
+ private:
+  const base::TimeDelta default_initial_backoff_;
+  const base::TimeDelta short_initial_backoff_;
+
+  DISALLOW_COPY_AND_ASSIGN(BackoffDelayProvider);
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_BACKOFF_DELAY_PROVIDER_H_