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This CL removes the Learn more row button in the Content settings and
puts that functionality in a new help button in the upper right of the
subpage.

BUG=658060
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://chromiumcodereview.appspot.com/2432383005
Cr-Commit-Position: refs/heads/master@{#426941}