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Use the API that's defined in native_client/src/public/.  That is
already used by nacl_listener.cc, but the code in nacl_ipc_adapter.cc
was written earlier, before the API in public/ was added.

NaClDescCreateWithFilePathMetadata() does the same as the code we're
replacing here.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=4073
TEST=browser_tests

Review URL: https://codereview.chromium.org/897363002

Cr-Commit-Position: refs/heads/master@{#315049}