initial version of the headless download manager delegate

This cl implementes setDownloadBehavior devtools command, for both headles/non-headless


BUG=696481

Change-Id: Ib4385e478e89219062241983a6ceb523bf476d09
Reviewed-on: https://chromium-review.googlesource.com/590913
Commit-Queue: David Vallet <dvallet@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496577}
12 files changed