Update testing tools (AppRTC, Go) to new versions

App engine is included in the AppRTC archive, so the separate archive is not needed anymore.
Mercurial is no longer necessary to include but it will be required during the vendoring step when the prebuilt archives are update.

The download/build scripts have been simplified accordingly.

The video quality test has been updated to work with the new appengine.

BUG=webrtc:7602

Review-Url: https://codereview.webrtc.org/2882073003
Cr-Commit-Position: refs/heads/master@{#18162}
diff --git a/webrtc/tools/testing/download_apprtc.py b/webrtc/tools/testing/download_apprtc.py
new file mode 100755
index 0000000..f6db785
--- /dev/null
+++ b/webrtc/tools/testing/download_apprtc.py
@@ -0,0 +1,58 @@
+#!/usr/bin/env python
+# Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+"""Downloads prebuilt AppRTC and Go from WebRTC storage and unpacks it.
+
+Requires that depot_tools is installed and in the PATH.
+
+It downloads compressed files in the directory where the script lives.
+This is because the precondition is that the script lives in the same
+directory of the .sha1 files.
+"""
+
+import os
+import sys
+
+import utils
+
+
+SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+
+
+def _GetGoArchivePathForPlatform():
+  archive_extension = 'zip' if utils.GetPlatform() == 'win' else 'tar.gz'
+  return os.path.join(utils.GetPlatform(), 'go.%s' % archive_extension)
+
+
+def main(argv):
+  if len(argv) > 2:
+    return 'Usage: %s [output_dir]' % argv[0]
+
+  output_dir = os.path.abspath(argv[1]) if len(argv) > 1 else None
+
+  apprtc_zip_path = os.path.join(SCRIPT_DIR, 'prebuilt_apprtc.zip')
+  if os.path.isfile(apprtc_zip_path + '.sha1'):
+    utils.DownloadFilesFromGoogleStorage(SCRIPT_DIR, auto_platform=False)
+
+  if output_dir is not None:
+    utils.RemoveDirectory(os.path.join(output_dir, 'apprtc'))
+    utils.UnpackArchiveTo(apprtc_zip_path, output_dir)
+
+  golang_path = os.path.join(SCRIPT_DIR, 'golang')
+  golang_zip_path = os.path.join(golang_path, _GetGoArchivePathForPlatform())
+  if os.path.isfile(golang_zip_path + '.sha1'):
+    utils.DownloadFilesFromGoogleStorage(golang_path)
+
+  if output_dir is not None:
+    utils.RemoveDirectory(os.path.join(output_dir, 'go'))
+    utils.UnpackArchiveTo(golang_zip_path, output_dir)
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))