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
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+// 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 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)
+      => (string thumbnail_data, gfx.mojom.Size original_size);
+};