Avoid default arguments at ThrottlingURLLoader

As the number of callers is not big, let's not use default arguments for
code health.

Another motivation of this CL is that we (people working on schedulers)
would like to do our local experiment to investigate task runner usages:
we plan to add an argument base::Location to TTRH::Get() and collect the
data on our local machine. Replacing TTRH::Get() with e.g.
TTRH::Get(FROM_HERE) would not be simple without this CL since we can't
compile default arguments' arguments.

Change-Id: I305cc3def1f24035ceb303019e35dcc0fa2b849e
Reviewed-on: https://chromium-review.googlesource.com/792318
Reviewed-by: Kinuko Yasuda <[email protected]>
Reviewed-by: Alexander Timin <[email protected]>
Commit-Queue: Hajime Hoshi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#519781}
4 files changed