./BUILD.gn has a target both_gn_and_gyp that's supposed to pull in all test binaries (roughly; see comment at top of file).

It lists many many tests in two nested ifs that aren't entered on mac (or cros):

  if (is_android || is_win || (is_linux && !is_chromeos)) {
    deps += [
      "//base:build_utf8_validator_tables",
      "//base:check_example",
      "//cc:cc_perftests",
      "//cc/blink:cc_blink_unittests",
      "//components:components_perftests",
      "//device:device_unittests",
      "//gin:gin_shell",
      "//gin:gin_unittests",
      "//google_apis/gcm:mcs_probe",
      "//gpu:gl_tests",
      "//gpu:gpu_perftests",
      "//ipc:ipc_perftests",
      "//media:media_perftests",
      "//net:dump_cache",
      "//sync:run_sync_testserver",
      "//third_party/codesighs:maptsvdifftool",
      "//third_party/libphonenumber:libphonenumber_unittests",
      "//ui/compositor:compositor_unittests",
    ]

    # TODO(GYP): Figure out which of these should (and can) build
    # for chromeos/mac/ios.
    if (!is_android) {
      ....


Most of these should be hooked up on mac as well.