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This CL only turns on the non-nullable check for validation tests.

There will be separate CLs for:
- add DCHECK at the sending side.
- make the existing APIs pass the non-nullable check and turn on the check everywhere.

BUG=324170
TEST=New and revised validation tests.

Review URL: https://codereview.chromium.org/466613002

Cr-Commit-Position: refs/heads/master@{#290002}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290002 0039d316-1c4b-4281-b951-d872f2087c98