Reason for revert:
Try to fix the webrtc/test/fuzzers issue and reland this CL because it
contains lots of fixes for our BUILD.gn files.
Original issue's description:
> Revert of Enable GN check for webrtc/base (patchset #13 id:240001 of https://codereview.webrtc.org/2717083002/ )
>
> Reason for revert:
> Breaks Chromium because in Chromium we import WebRTC with rtc_include_tests=false (https://bugs.chromium.org/p/chromium/issues/detail?id=713179#c6).
>
> Chromium uses webrtc/test/fuzzers and this CL adds test dependencies to neteq_rtc_fuzzer.
>
> Original issue's description:
> > Enable GN check for webrtc/base
> >
> > It's not possible to enable it for the rtc_base_approved
> > target but since a larger refactoring is ongoing for webrtc/base
> > this CL doesn't attempt to fix that.
> >
> > Changes made:
> > * Move webrtc/system_wrappers/include/stringize_macros.h into
> > webrtc/base:rtc_base_approved_unittests (and corresponding
> > unit test to rtc_base_approved_unittests).
> > * Move md5digest.* from rtc_base_approved to rtc_base_test_utils target.
> > * Move webrtc/system_wrappers/include/stringize_macros.h (+test) into
> > webrtc/base.
> > * Remove unused use include of webrtc/base/fileutils.h in
> > webrtc/base/pathutils.cc
> >
> > BUG=webrtc:6828, webrtc:3806, webrtc:7480
> > NOTRY=True
> >
> > Review-Url: https://codereview.webrtc.org/2717083002
> > Cr-Commit-Position: refs/heads/master@{#17766}
> > Committed: ed754e71ae
>
> TBR=perkj@webrtc.org,tommi@webrtc.org,nisse@webrtc.org,kjellander@webrtc.org
> # Not skipping CQ checks because original CL landed more than 1 days ago.
> BUG=webrtc:6828, webrtc:3806, webrtc:7480
> NOTRY=True
>
> Review-Url: https://codereview.webrtc.org/2838683002
> Cr-Commit-Position: refs/heads/master@{#17849}
> Committed: 11ed366c48TBR=perkj@webrtc.org,tommi@webrtc.org,nisse@webrtc.org,kjellander@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:6828, webrtc:3806, webrtc:7480
Review-Url: https://codereview.webrtc.org/2840453004
Cr-Commit-Position: refs/heads/master@{#17876}
7054085e59