[DEPS] Add libprotobuf-mutator as a new dependency

Change-Id: Ifb0cb604a9eedb9d4a42c1040930288ede940df5
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/189711
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/DEPS b/DEPS
index 17c9e5c..7b9cd5c 100644
--- a/DEPS
+++ b/DEPS
@@ -423,6 +423,11 @@
     'condition': 'dawn_standalone',
   },
 
+  'third_party/libprotobuf-mutator/src': {
+    'url': '{chromium_git}/external/github.com/google/libprotobuf-mutator.git@a304ec48dcf15d942607032151f7e9ee504b5dcf',
+    'condition': 'dawn_standalone',
+  },
+
   # Dependencies for tintd.
   'third_party/jsoncpp': {
     'url': '{github_git}/open-source-parsers/jsoncpp.git@69098a18b9af0c47549d9a271c054d13ca92b006',