Roll third_party/zlib/ 21c6af6f1..a68151fd9 (11 commits)

https://chromium.googlesource.com/chromium/src/third_party/zlib.git/+log/21c6af6f18e5..a68151fd9b9f

Created with:
  roll-dep third_party/zlib

Change-Id: I2582bd67c7fe3abb636c4b6c5b3023da7f2ad2ca
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/70371
Commit-Queue: Alan Screen <awscreen@chromium.org>
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>

DEPS

diff --git a/DEPS b/DEPS
index 962953e..363fb33 100644
--- a/DEPS
+++ b/DEPS
@@ -99,7 +99,7 @@
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling zlib
   # and whatever else without interference from each other.
-  'zlib_revision': '21c6af6f18e5ad9c3b9d103f8cfdbf926ca35f7c',
+  'zlib_revision': 'a68151fd9b9f5ad11b96a3765f706361ff22dbc8',
 }
 
 deps = {