This is a purely cosmetic change. Rename all local variables and
parameters of type CallDescriptor* to "call_descriptor".
For locals that are now named "call_descriptor", use auto upon
initialization, following the Google style guide
(https://google.github.io/styleguide/cppguide.html#auto).

Note: fields in structs and classes were not renamed in this CL.

R=clemensh@chromium.org,mstarzinger@chromium.org,jarin@chromium.org

Change-Id: Ic6f7afdba12f7b97741b098a9d0e0f58c41c587e
Reviewed-on: https://chromium-review.googlesource.com/909866
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51223}