Add fuzzer for PasswordGenerator.

This fuzzer passes fuzzed message |PasswordRequirementsSpec| to function |GeneratePassword|.
The random choices inside the function are still random and not replaced by the fuzzed input.

R=vabr@chromium.org

Bug: 847200
Change-Id: I221fe286328d5818bd50282046799e8930079298
Reviewed-on: https://chromium-review.googlesource.com/1120088Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Vaclav Brozek <vabr@chromium.org>
Commit-Queue: Vaclav Brozek <vabr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584059}

components/autofill/core/browser/BUILD.gn

@@ -116,8 +116,6 @@ jumbo_static_library("browser") {
     "local_card_migration_manager.h",
     "name_field.cc",
     "name_field.h",
-    "password_generator.cc",
-    "password_generator.h",
     "password_requirements_spec_fetcher.h",
     "password_requirements_spec_fetcher_impl.cc",
     "password_requirements_spec_fetcher_impl.h",
@@ -255,6 +253,7 @@ jumbo_static_library("browser") {
     "//third_party/libaddressinput",
   ]
   deps = [
+    ":password_generator",
     ":password_generator_fips181",
     "//base",
     "//base:i18n",
@@ -373,6 +372,19 @@ jumbo_static_library("test_support") {
   ]
 }
 
+static_library("password_generator") {
+  sources = [
+    "password_generator.cc",
+    "password_generator.h",
+  ]
+  public_deps = [
+    "//components/autofill/core/browser/proto",
+  ]
+  deps = [
+    "//base",
+  ]
+}
+
 static_library("password_generator_fips181") {
   sources = [
     "password_generator_fips181.cc",
@@ -494,6 +506,7 @@ source_set("unit_tests") {
 
   deps = [
     ":browser",
+    ":password_generator",
     ":password_generator_fips181",
     ":test_support",
     ":unit_tests_bundle_data",
@@ -572,4 +585,15 @@ if (use_libfuzzer) {
       "//third_party/libprotobuf-mutator",
     ]
   }
+
+  fuzzer_test("password_generator_proto_fuzzer") {
+    sources = [
+      "password_generator_proto_fuzzer.cc",
+    ]
+    deps = [
+      ":password_generator",
+      "//components/autofill/core/browser/proto",
+      "//third_party/libprotobuf-mutator",
+    ]
+  }
 }

components/autofill/core/browser/password_generator_proto_fuzzer.cc

+// Copyright 2018 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 "components/autofill/core/browser/password_generator.h"
+#include "components/autofill/core/browser/proto/password_requirements.pb.h"
+#include "testing/libfuzzer/proto/lpm_interface.h"
+
+namespace autofill {
+
+DEFINE_PROTO_FUZZER(const PasswordRequirementsSpec& spec) {
+  GeneratePassword(spec);
+}
+
+}  // namespace autofill

components/password_manager/core/browser/BUILD.gn

@@ -188,6 +188,7 @@ jumbo_static_library("browser") {
     ":proto",
     "//base:i18n",
     "//components/autofill/core/browser",
+    "//components/autofill/core/browser:password_generator",
     "//components/autofill/core/browser/proto",
     "//components/autofill/core/common",
     "//components/favicon/core",