Implement BackgroundFetchManager.fetch() and struct traits

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
 };
 
 struct IconDefinition {

[dcheng, 2017/03/21 07:03:20]

It would be nice to point at the spec definition for these as appropriate, so
it's clear what the contents of the different fields can be. In particular, it
seems like these fields might need some sort of parsing, which always warrants
extra scrutiny (is it possible / does it make sense to parse it in Blink?)

[Peter Beverloo, 2017/03/21 13:46:27]

I've added links to their specifications. The links now occur in the code three
times for each type, but it should help people create a mental model of the
code. In the mid-term this'll move elsewhere, we're just not quite sure yet
where. (Other specs will use it too.)

We need to do two things with these values:
  (1) Fetch an appropriate image to use in the notification associated with the
background fetch. This will happen through an image loader in Blink, where we'll
also parse its values.
  (2) Store them and give them back to the developer when they get a
BackgroundFetchRegistration.

As such, we don't actually use or parse the values themselves in the browser, we
merely store them. I've extended the comment in background_fetch_types.h to
explain this intent.

   string src;
   string sizes;
   string type;
 };
 
+struct BackgroundFetchOptions {
+  array<IconDefinition> icons;
+  int64 total_download_size;
+  string title;
+};
+
 struct BackgroundFetchRegistration {
   string tag;
   array<IconDefinition> icons;
-  int64 total_download_size = 0;
-  string title = "";
+  int64 total_download_size;
+  string title;
 };
 
 interface BackgroundFetchService {
-  // TODO(peter): Implement support for the `fetch()` function in Mojo.
+  // Creates a new Background Fetch registration identified by |tag| with the
+  // given |options| for the sequence of |requests|.
+  Fetch(int64 service_worker_registration_id,
+        string tag,
+        BackgroundFetchOptions options)
+      => (BackgroundFetchError error,
+          BackgroundFetchRegistration? registration);
 
   // 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);
 };