Fix public dependency in components/arc
Fix public dependency in components/arc

The mojom target should be in public_deps, since public component headers
(e.g. arc_bridge_service.h) depend on the mojom being generated. Without
this, dependents can flakily fail to build.

BUG=None
R=elijahtaylor@chromium.org

Review URL: https://codereview.chromium.org/1527133002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#365620}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk