Re-revert of "Remove SSLClientAuthHandler's RDH dependency." (https://codereview...

Re-revert of "Remove SSLClientAuthHandler's RDH dependency." (https://codereview.chromium.org/596873002)

Reason for revert:
Causes browser crash if URL request is cancelled during client cert loading.

This is a reland of https://codereview.chromium.org/766463002/ which reverted
https://codereview.chromium.org/596873002. The revert was reverted because it
introduced a memory leak.

The source of this memory leak was a reference cycle in
chrome/browser/chromeos/net/client_cert_filter_chromeos.cc whose fix is
included in this CL. If InitIfSlotsAvailable returns true (synchronously), the
callback should not be retained. This was not a problem before as the code in
question was introduced after https://codereview.chromium.org/596873002 which
unrefcounted an object.

After this is merged into M-40, https://codereview.chromium.org/596873002
should be reworked with the crash fixed as this reference cycle is too subtle
and the object really needn't be reference-counted.

TBR=mmenke@chromium.org,benm@chromium.org,jam@chromium.org

BUG=422765, 427844, 376003

Review URL: https://codereview.chromium.org/773003004

Cr-Commit-Position: refs/heads/master@{#306649}