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- Add libcronet.so to cronet_tests rpath.
- Use trivial ProxyResolutionService to avoid crashes.

Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I3a114b098a4d78e4087be948dfd3ce303d6df737
Bug: 813226
Reviewed-on: https://chromium-review.googlesource.com/987521Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Misha Efimov <mef@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547521}