[Passwords] Add Fuzzer for Leak Detection

This change adds a simple fuzzer for CipherEncrypt() used in the Leak
Detection feature.

Bug: 986298
Change-Id: I4878b1bf04a0edc4341c7c2997e443207120d6d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1763756
Commit-Queue: Vasilii Sukhanov <vasilii@chromium.org>
Auto-Submit: Jan Wilken Dörrie <jdoerrie@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689510}

components/password_manager/core/browser/leak_detection/BUILD.gn

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/jumbo.gni")
+import("//testing/libfuzzer/fuzzer_test.gni")
 import("//third_party/libprotobuf-mutator/fuzzable_proto_library.gni")
 
 fuzzable_proto_library("proto") {
@@ -95,3 +96,12 @@ jumbo_source_set("unit_tests") {
     "//third_party/private-join-and-compute/src:ec_commutative_cipher",
   ]
 }
+
+fuzzer_test("encryption_utils_fuzzer") {
+  sources = [
+    "cipher_encrypt_fuzzer.cc",
+  ]
+  deps = [
+    ":leak_detection",
+  ]
+}

components/password_manager/core/browser/leak_detection/cipher_encrypt_fuzzer.cc

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <string>
+
+#include "components/password_manager/core/browser/leak_detection/encryption_utils.h"
+
+namespace password_manager {
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  std::string payload(reinterpret_cast<const char*>(data), size);
+  std::string key;
+  std::string cipher = password_manager::CipherEncrypt(payload, &key);
+  return 0;
+}
+
+}  // namespace password_manager