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In document mode, we used to start loading the web contents of a newly
opened tab before the chrome tab object is ready. This would result in
chrome intercept delegate not being initialized in time to figure out
whether the loaded URL needs to be sent as an intent instead.

This changes the order of operations to create the chrome tab first with
the given web contents and only then initiate the load.

BUG=432562

Review URL: https://codereview.chromium.org/883153002

Cr-Commit-Position: refs/heads/master@{#313966}