Defines initial inner circle of interfaces for background offlining.

components/offline_pages/background_request_coordinator.h

Index: components/offline_pages/background_request_coordinator.h
diff --git a/components/offline_pages/background_request_coordinator.h b/components/offline_pages/background_request_coordinator.h
new file mode 100644
index 0000000000000000000000000000000000000000..bfa21436344f7552b0f086c8a960b0e641723f8c
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+++ b/components/offline_pages/background_request_coordinator.h
@@ -0,0 +1,34 @@
+// 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 COMPONENTS_OFFLINE_PAGES_BACKGROUND_REQUEST_COORDINATOR_H_
+#define COMPONENTS_OFFLINE_PAGES_BACKGROUND_REQUEST_COORDINATOR_H_
+
+namespace offline_pages {
+
+class SavePageRequest;
+
+// Coordinates queueing and processing save page later requests.
+class BackgroundRequestCoordinator {
+ public:
+  // Callback to report when the processing of a triggered task is complete.
+  typedef base::Callback<void()> ProcessingDoneCallback;
+
+  virtual ~BackgroundRequestCoordinator() {}
+
+  // Queues |request| to later load and save when system conditions allow.
+  virtual bool SavePageLater(const SavePageRequest& request) = 0;
+
+  // Starts processing of one or more queued save page later requests.

[Dmitry Titov, 2016/04/26 00:20:31]

Consider adding comments on:
- can StartProcessing be called multiple times (while processing is udnerway) or
are subsequent calls ignored, or callback is invoked with some
ALREADY_IN_PROGRESS indicator
- Is StopProcessing always guaranteed to be called pair-wise with
StartProcessing?
- Must ProcessingDone be called in response to StopProcessing or is in fact it's
other way around, and ProcessingDone callback actually causes the
StopProcessing?
- If StopProcessing is optional (conditions changed on the device) then should
callback be called only if StopProcessing is not invoked?
- Can this class process multiple requests or is ti one URL per 'processing'?

[dougarnett, 2016/04/26 15:50:38]

Please check updated wording on Start/Stop. 
Btw, the first sentence of Start does already say "one or more" so think I have
last point covered so if not clear please suggest how to make more clear.

+  virtual void StartProcessing(const ProcessingDoneCallback& callback) = 0;
+
+  // Stops the current request processing if active.
+  virtual void StopProcessing() = 0;
+
+  // TODO(dougarnett): add policy support methods.
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_BACKGROUND_REQUEST_COORDINATOR_H_