Explicitly set a requestor origin when calling into WebLocalFrame::loadRequest

Various tests (and, in particular, the testrunner itself) use loadRequest
as a shortcut around various bits of the loading infrastructure. This patch
has zero web-visible impact, but will ensure that the DCHECK I'd like to add
in https://codereview.chromium.org/2128503002 doesn't cause most tests to
explode.

BUG=625969
R=jochen@chromium.org

Review-Url: https://codereview.chromium.org/2125263002
Cr-Commit-Position: refs/heads/master@{#404135}
7 files changed