A std::deque interacts badly with zone memory in that it allocates chunks
of memory for the back of the queue and frees memory from the front of the
queue. As such we never reuse zone memory for the queue. Implement a very
simple RecyclingZoneAllocator which keeps a single block of memory from
deallocation that can be reused on allocation.

Also clean up zone-allocator a bit and make it use proper Chromium coding
style.

BUG=chromium:700364

Change-Id: I19330a8a9ec6d75fe18d8168d41f1a12030a6c4d
Reviewed-on: https://chromium-review.googlesource.com/458916Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44154}