Implement a Mojo service for Background Fetch

third_party/WebKit/public/platform/modules/background_fetch/background_fetch.mojom

+// 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.
+
+module blink.mojom;
+
+enum BackgroundFetchError {
+  NONE,
+  DUPLICATED_TAG

[harkness, 2017/03/14 11:55:47]

Why not add in NOT_YET_IMPLEMENTED now? It would be appropriate for many of the
calls, and will still be appropriate in the future when there are calls in v2
that are not implemented in v1.

Also, I'm not sure what your intention for DUPLICATED_TAG is. It makes sense for
fetch(), but not for any of the other methods. For Abort/GetRegistration, it
seems like NO_TAG (INVALID_TAG? but that feels like a syntax issues) would be a
better error.

[Peter Beverloo, 2017/03/14 15:17:21]

We shouldn't expose any method that's not implemented yet, which is why the
status of the feature is "test": even the "Experimental Web Platform Features"
flag doesn't capture it yet.

This enum will likely be used for UMA too, so there's a cost to adding values
(we won't be able to remove them).
See my previous comment on generic vs. individual enums.

[harkness, 2017/03/14 17:17:29]

re: Not yet implemented - ok

re: DUPLICATED_TAG

I don't have an issue with either the generic or the individual enum, I think
either approach is reasonable. 

I suppose my real issue here is that while DUPLICATED_TAG makes sense as a
return value for fetch(), it doesn't make any sense to me as an error code for
get() which is where you're currently returning it. 

[Peter Beverloo, 2017/03/14 17:28:15]

Ahh got it. Done!

+};
+
+struct IconDefinition {
+  string src;
+  string sizes;
+  string type;
+};
+
+struct BackgroundFetchRegistration {
+  string tag;
+  array<IconDefinition> icons;
+  int64 total_download_size = 0;
+  string title = "";
+};
+
+interface BackgroundFetchService {
+  // TODO(peter): Implement suppor for the `fetch()` function in Mojo.

[haraken, 2017/03/14 09:13:14]

support

[Peter Beverloo, 2017/03/14 15:17:21]

Done.

+
+  // Updates the user interface for the Background Fetch identified by the
+  // |service_worker_registration_id| and the |tag|.
+  UpdateUI(int64 service_worker_registration_id, string tag, string title)
+      => (BackgroundFetchError error);
+
+  // Aborts the Background Fetch registration identified by the
+  // |service_worker_registration_id| and the |tag|.
+  Abort(int64 service_worker_registration_id, string tag);
+
+  // Gets the Background Fetch registration identified by the
+  // |service_worker_registration_id| and the |tag|.
+  GetRegistration(int64 service_worker_registration_id, string tag)
+      => (BackgroundFetchError error,
+          BackgroundFetchRegistration? registration);
+
+  // Gets the sequence of tags for active Background Fetch registrations given
+  // the |service_worker_registration_id|.
+  GetTags(int64 service_worker_registration_id)
+      => (BackgroundFetchError error,
+          array<string> tags);
+};