Don't use fuzzer_test() outside of Chromium

Makes dependency on //testing/libfuzzer/fuzzer_test.gni conditional on
build_with_chromium. This makes it easier to build //third_party/libpng
outside of a Chromium checkout, such as within PDFium.

Bug: 1130821
Change-Id: I2e1e1e68f0b2d7483939b9f55881d37626bf8eed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4027672
Commit-Queue: Leon Scroggins <scroggo@google.com>
Commit-Queue: K. Moon <kmoon@chromium.org>
Auto-Submit: K. Moon <kmoon@chromium.org>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Cr-Commit-Position: refs/heads/main@{#1071807}
NOKEYCHECK=True
GitOrigin-RevId: 82ebc504d85dcfcdacfa828c4a2ef4ff650f6b1d
1 file changed