mojo: Fix target type in platform handle's gyp files.
mojo: Fix target type in platform handle's gyp files.

BUG=585587

Review URL: https://codereview.chromium.org/1723393002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#377321}

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