Replace image_messages.h with Mojo service

content/common/image_downloader/image_downloader.mojom

+// Copyright 2015 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 image_downloader;
+
+import "skia/public/interfaces/bitmap.mojom";
+import "ui/mojo/geometry/geometry.mojom";
+
+struct DownloadRequest {
+  string url;
+  bool is_favicon;
+  uint32 max_bitmap_size;
+  bool bypass_cache;
+};
+
+struct DownloadResult {
+  int32 http_status_code;
+  array<skia.Bitmap> images;
+  array<mojo.Size> original_image_sizes;
+};
+
+interface ImageDownloader {
+  // Fetch and decode an image from a given URL.
+  // Returns the decoded images, or http_status_code to indicate error.
+  // Each call is independent, overlapping calls are possible.
+  DownloadImage(DownloadRequest request) => (DownloadResult result);
+};