Mojoify the RequestThumbnailForContextNode IPC message and reply

chrome/common/thumbnail_capturer.mojom

Index: chrome/common/thumbnail_capturer.mojom
diff --git a/chrome/common/thumbnail_capturer.mojom b/chrome/common/thumbnail_capturer.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..71bf82c2777c403aa95c1ad8b3fed1626c8be20b
--- /dev/null
+++ b/chrome/common/thumbnail_capturer.mojom
@@ -0,0 +1,18 @@
+// 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 chrome.mojom;
+
+import "ui/gfx/geometry/mojo/geometry.mojom";
+
+interface ThumbnailCapturer {
+  // Requests a JPEG encoded thumbnail of the image selected by the most
+  // recently opened context menu. If no image is selected or there's an error
+  // capturing a thumbnail, |thumbnail_data| will be empty. If the image area is
+  // larger than |thumbnail_min_area_pixels| it will be downscaled to fit within
+  // |thumbnail_max_size_pixels|.
+  RequestThumbnailForContextNode(int32 thumbnail_min_area_pixels,
+                                 gfx.mojom.Size thumbnail_max_size_pixels)
+      => (array<uint8> thumbnail_data, gfx.mojom.Size original_size);
+};