[Offline Prefetch] Send GeneratePageBundleRequest to the server

components/offline_pages/core/prefetch/proto/operation.proto

+// 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.
+
+syntax = "proto3";
+option optimize_for = LITE_RUNTIME;
+
+package offline_pages.proto;
+;
+
+import "any.proto";
+import "status.proto";
+
+// This resource represents a long-running operation that is the result of a
+// network API call.
+message Operation {
+  // The server-assigned name, which is only unique within the same service that
+  // originally returns it.
+  string name = 1;
+
+  // Service-specific metadata associated with the operation.  It typically
+  // contains progress information and common metadata such as create time.
+  // Some services might not provide such metadata.  Any method that returns a
+  // long-running operation should document the metadata type, if any.
+  Any metadata = 2;
+
+  // If the value is 'false', it means the operation is still in progress.
+  // If true, the operation is completed, and either 'error' or 'response' is
+  // available.
+  bool done = 3;
+
+  // The operation result, which can be either an 'error' or a valid 'response'.
+  // If 'done' == 'false', neither 'error' nor 'response' is set.
+  // If 'done' == 'true', exactly one of 'error' or 'response' is set.
+  oneof result {
+    // The error result of the operation in case of failure or cancellation.
+    Status error = 4;
+
+    // The normal response of the operation in case of success.
+    Any response = 5;
+  }
+}