Unify multiple ways to construct DocumentLoader

This patch moves all logic related to constructing
DocumentLoader to it's constructor. It also removes
the methods which we only need when creating
a DocumentLoader.

Bug: 855189
Change-Id: I32521ab453b78c80e3f8266d07eb5a1268df0786
Reviewed-on: https://chromium-review.googlesource.com/c/1274836
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601842}
10 files changed