GN: Add an assert for proper output directory nesting on Android
GN: Add an assert for proper output directory nesting on Android

BUG=412935

Review URL: https://codereview.chromium.org/1406173004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#356919}

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