Add webrtc/rtc_base in preparation for the larger rename in https://codereview.webrtc.org/2877023002. This is needed in order to make downstream projects update their dependencies (since it's not possible to use public_deps for android_library). BUG=webrtc:7634 NOTRY=True Change-Id: I90fa72c9ebbc4e69bb3133413c3258432a5a72b1 Reviewed-on: https://chromium-review.googlesource.com/541215 Reviewed-by: Tommi <tommi@webrtc.org> Commit-Queue: Henrik Kjellander <kjellander@webrtc.org> Cr-Commit-Position: refs/heads/master@{#18699}