Oilpan: Do not include wtf/functional.h

No one in platform/heap/ needs wtf/functional.h, though persistent.h
needs base/bind.h for IsWeakReceiver<> and BindUnwrapTraits<>.

This CL reduces the pre-processed size of handle.h by 31KB.

Bug: 242216
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I6097a6f22dbe7a762f4b0a23560c731a07daf5ce
Reviewed-on: https://chromium-review.googlesource.com/1134809
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574536}
26 files changed