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 {
+  // Called by ImageDownloaderDispatcher, sends download request

[Anand Mistry (off Chromium), 2015/06/12 08:19:38]

This is an interface. Describe the intended functionality, not the
implementation. i.e.
Fetch and decode an image from a given URL. Returns the decoded image.

But add a bit more detail than that.

[leonhsl(Using Gerrit), 2015/06/15 08:09:43]

Done.

+  // and receives async download result.
+  // Implemented by ImageDownloaderImpl to fetch image data actually.
+  // Each call is independent, overlapping calls are possible.
+  DownloadImage(DownloadRequest request) => (DownloadResult result);
+};