Enable "gn check" for //third_party/blink/renderer/modules/manifest

This CL has no behavior changes.

Bug: 800764
Change-Id: I2d3c4b1ee953d4cc7581db2c5d0c0ebbeb7f7123
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2400583


Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805613}