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Tested with the following command lines on Linux:

$ gn gen out-gn --args=enable_nacl=true
$ ninja -C out-gn nacl_loader_unittests

Note: There are still many link errors with this target. They will be
addressed in followup patches.

BUG=432959
TEST=see above
R=bradn@google.com,dpranke@chromium.org
TBR=bradnelson@chromium.org

Review URL: https://codereview.chromium.org/1034723002

Cr-Commit-Position: refs/heads/master@{#322365}