Reverting http://crrev.com/c/1545366.

Restoring |pending_state_map_| and the code that posts a task to the IO
thread to destroy the SecurityState because we get a lot of
RenderFrameMessageFilter::GetCookies() and
RenderFrameMessageFilter::SetCookies() crashes without this.

Change-Id: Ia6d483f91eda89f38779e88bf8cb17565870bfbb
Bug: 943887
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1554407
Commit-Queue: Aaron Colwell <acolwell@chromium.org>
Auto-Submit: Aaron Colwell <acolwell@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648331}