Use subprocess2 and DEPS-pinned depot_tools for download_tools.py
Use subprocess2 and DEPS-pinned depot_tools for download_tools.py

As https://webrtc.googlesource.com/src/+/915187b1afe8f708b06e24b77f372dcd34fe75f3
has the proper fixed rolled in, https://webrtc-review.googlesource.com/c/src/+/8820
can be relanded to benefit from using DEPS-pinned third_party/depot_tools instead
of the auto-updated one.

TBR=mbonadei@webrtc.org

Bug: chromium:773671, webrtc:8393
Change-Id: Id47671956d014ce24e5b60ce3aae5423930db1aa
No-try: True
Reviewed-on: https://webrtc-review.googlesource.com/10800
Commit-Queue: Henrik Kjellander <60c11d3e646624f25a02b88f51d51ca6b7ff7c72@webrtc.org>
Reviewed-by: Henrik Kjellander <60c11d3e646624f25a02b88f51d51ca6b7ff7c72@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#20301}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc