Add the download component and initial setup

components/download/public/download_params.h

Index: components/download/public/download_params.h
diff --git a/components/download/public/download_params.h b/components/download/public/download_params.h
new file mode 100644
index 0000000000000000000000000000000000000000..7a94dc39e61c1716a998c7250e2cd1dc9556bb6a
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+++ b/components/download/public/download_params.h
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+// 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_DOWNLOAD_PUBLIC_DOWNLOAD_PARAMS_H_
+#define COMPONENTS_DOWNLOAD_PUBLIC_DOWNLOAD_PARAMS_H_
+
+#include "base/callback.h"
+#include "base/time/time.h"
+#include "components/download/public/clients.h"
+#include "net/http/http_request_headers.h"
+#include "url/gurl.h"
+
+namespace download {
+
+// The parameters describing when to run a download.  This allows the caller to
+// specify restrictions on what impact this download will have on the device
+// (battery, network conditions, priority, etc.).
+struct SchedulingParams {
+ public:
+  enum NetworkRequirements {
+    // The download can occur under all network conditions.
+    NONE = 0,
+
+    // The download should occur when the network isn't metered.  However if the
+    // device does not provide that opportunity over a long period of time, the
+    // DownloadService may start allowing these downloads to run on metered
+    // networks as well.
+    OPTIMISTIC = 1,

[Peter Beverloo, 2017/05/02 16:12:21]

nit: the user would use this value as SchedulingParams::OPTIMISTIC, which does
not convey that it's just about the network requirements. Usually we use one of
these two:

  1) enum class
  2) prefix with type, NETWORK_REQUIREMENTS_OPTIMISTIC

[David Trainor- moved to gerrit, 2017/05/03 06:02:59]

ah enum class is nice thanks!

+
+    // The download can occur only if the network isn't metered.
+    UNMETERED = 2,
+  };
+
+  enum BatteryRequirements {
+    // The download can only occur when charging or in optimal battery
+    // conditions.
+    BATTERY_SENSITIVE = 0,

[xingliu, 2017/05/01 23:56:54]

nit: Can we put BATTERY_INSENSITIVE before BATTERY_SENSITIVE? Since network
requirement and priority are sorted from loose to strict.

[David Trainor- moved to gerrit, 2017/05/03 06:02:59]

Done.

+
+    // The download can occur under all battery scenarios.  Note that the
+    // DownloadService may still not run this download under extremely low
+    // battery conditions.
+    BATTERY_INSENSITIVE = 1,
+  };
+
+  enum Priority {
+    // The lowest priority.  Requires that the device is idle or Chrome is
+    // running.
+    LOW = 0,
+
+    // The normal priority.  Requires that the device is idle or Chrome is
+    // running.
+    NORMAL = 1,
+
+    // The highest background priority.  Does not require the device to be idle.
+    HIGH = 2,
+
+    // The highest priority.  This will act (scheduling requirements aside) as a
+    // user-initiated download.
+    UI = 3,
+
+    // The default priority for all tasks unless overridden.
+    DEFAULT = NORMAL,
+  };
+
+  SchedulingParams();
+  ~SchedulingParams() = default;
+
+  // Cancel the download after this delay.  Will cancel in-progress downloads.
+  base::TimeDelta cancel_after;
+
+  // The suggested priority.  Non-UI priorities may not be honored by the
+  // DownloadService based on internal criteria and settings.
+  Priority priority;
+  NetworkRequirements network_requirements;
+  BatteryRequirements battery_requirements;
+};
+
+// The parameters describing how to build the request when starting a download.
+struct RequestParams {
+ public:
+  RequestParams();
+  ~RequestParams() = default;
+
+  GURL url;
+
+  // The request method ("GET" is the default value).
+  std::string method;
+  net::HttpRequestHeaders request_headers;

[xingliu, 2017/05/01 23:56:54]

nit: Not necessary in this patch, but shall we avoid to copy DownloadParam in
the future because of |request_headers|?

[David Trainor- moved to gerrit, 2017/05/03 06:02:59]

Will that cause an issue?  I did add copy constructors to these structs though.

+};
+
+// The parameters that describe a download request made to the
+// BackgroundDownloadService.  The |client| needs to be properly created and
+// registered for this service for the download to be accepted.
+struct DownloadParams {
+  enum StartResult {
+    // The download is accepted and persisted.
+    ACCEPTED,
+
+    // The DownloadService has too many downloads.  Backoff and retry.
+    BACKOFF,
+
+    // Failed to create the download.  Invalid input parameters.
+    BAD_PARAMETERS,
+
+    // TODO(dtrainor): Add more error codes.
+  };
+
+  DownloadParams();
+  ~DownloadParams();
+
+  // The feature that is requesting this download.
+  DownloadClient client;
+
+  // A unique GUID that represents this download.  See |base::GenerateGUID()|.
+  std::string guid;
+
+  // A callback that will be notified if this download has been accepted and
+  // persisted by the DownloadService.
+  base::Callback<void(const DownloadParams&, StartResult)> callback;
+
+  // The parameters that determine under what device conditions this download
+  // will occur.
+  SchedulingParams scheduling_params;
+
+  // The parameters that define the actual download request to make.
+  RequestParams request_params;
+};
+
+}  // namespace download
+
+#endif  // COMPONENTS_DOWNLOAD_PUBLIC_DOWNLOAD_PARAMS_H_