Roll DEPS for zlib to 91155b5d.

Routine roll.
https://chromium.googlesource.com/chromium/src/third_party/zlib/+log/945bc9fb..91155b5d

TBR=dsinclair@chromium.org

Change-Id: I93a37bde12f44fa769abbef882ea04ebb8e05a8d
Reviewed-on: https://pdfium-review.googlesource.com/20910
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/DEPS b/DEPS
index cc8fc13..592e782 100644
--- a/DEPS
+++ b/DEPS
@@ -24,7 +24,7 @@
   'trace_event_revision': '0e9a47d74970bee1bbfc063c47215406f8918699',
   'v8_revision': 'ff3d8321d52d599a7ce168e20ade02e8ef131d0a',
   'yasm_source_revision': 'b98114e18d8b9b84586b10d24353ab8616d4c5fc',
-  'zlib_revision': '945bc9fbe26f06ea07308eee946b907735a75519',
+  'zlib_revision': '91155b5d0737713fc7f0499cf0ba2c4f2af24014',
 }
 
 deps = {