[clang-tidy] Readability fixes for src/components/[d-l].*

- Get rid of redundant .c_str() for std::string,
- Get rid of redundant .get() for std::unique_ptr,
- Get rid of redundant member initializations
- Replace NULL -> nullptr.

R=blundell@chromium.org, caitkp@chromium.org, jochen@chromium.org, sdefresne@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ic043a0bf296132eadd1b8a6e349d3a5f903fbaec
Reviewed-on: https://chromium-review.googlesource.com/1045965
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Alexander Yashkin <a-v-y@yandex-team.ru>
Cr-Commit-Position: refs/heads/master@{#559197}
56 files changed