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Previously each locale filename was passed separately on the command
line. This causes problems on Windows because of the 8K command line limit.

A follow-up cl will move the webapp filenames into separate files to reduce
the liklihood that we'll encounter this limit in the future.

BUG=

Review URL: https://codereview.chromium.org/905553002

Cr-Commit-Position: refs/heads/master@{#314966}