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This CL makes background style of "System Security Settings" look like
"Help App" background dialog that can be launched from the same UI.

BUG=604119,665752
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2648623002
Cr-Commit-Position: refs/heads/master@{#445024}