A tweak on importer to import webdriver/tests from upstream manually.

Prevent external/wpt/webdriver directory from being cleared out everytime importer imports WPT tests from upstream. This code will be reverted once we start on the two-way sync phase.

Bug: 881513
Change-Id: I6606277c77b66244dcdfb310ce139eba4087aa77
Reviewed-on: https://chromium-review.googlesource.com/c/1450396
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Kyle Ju <kyleju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628907}
2 files changed