Don't add <tempdir>/.empty file to every jar.
Don't add <tempdir>/.empty file to every jar.

Instead add <classes_dir>/.empty file if all classes are excluded.

BUG=496876

Review URL: https://codereview.chromium.org/1414053005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#355827}

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