Change CHECK into DCHECK.

Code in the browser process should not be doing a CHECK based on data
coming from the renderer process, as this allows a compromised renderer
to trivially kill the whole browser.

BUG=688425
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2721393002
Cr-Commit-Position: refs/heads/master@{#454047}
1 file changed