Account for device scale factor in automation API bounding boxes.

chrome/common/extensions/api/automation_api_constants.h

+// Copyright 2016 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.
+
+#ifndef CHROME_COMMON_EXTENSIONS_API_AUTOMATION_API_CONSTANTS_H_
+#define CHROME_COMMON_EXTENSIONS_API_AUTOMATION_API_CONSTANTS_H_
+
+namespace extensions {
+namespace api {
+namespace automation {
+
+// The accessibility tree ID of the desktop tree. All other tree IDs are
+// for web content.
+const int kDesktopTreeID = 0;
+
+}  // namespace automation
+}  // namespace api
+}  // namespace extensions
+
+#endif  // CHROME_COMMON_EXTENSIONS_API_AUTOMATION_API_CONSTANTS_H_