[third_party/pigweed] Roll 3 commits

5a521cb4f24cfd6 docs: Gerrit code coverage documentation
db39d89da115738 docs: Move copyright header info to style guide
7afbb205c205659 pw_allocator: Fix use-after-free in ~AllocatorForT

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 8750debc3c31d37..5a521cb4f24cfd6
Roller-URL: https://ci.chromium.org/b/8763041079030400449
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib773d4565204aeacf89aaf99c4839abdd698fc7c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/183108
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 8750deb..5a521cb 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 8750debc3c31d37b7896ecf896849c4545f44142
+Subproject commit 5a521cb4f24cfd6797fbb14d287ec5e90f452253