[Passwords] Add forward declaration for PasswordForm

This change adds a separate header for forward declarations of
password_manager::PasswordForm. Since this is currently only an alias of
autofill::PasswordForm, a naive forward declaration does not work.

Furthermore, this change creates a new target for password_form,
making it easier to split up cycling dependencies between several
password_manager sub components.

Bug: 1067347
Change-Id: Ia5e6cd83dfd84b09c7dd3069d4f86ca2830102fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2426449
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810168}

components/password_manager/core/browser/BUILD.gn

@@ -148,7 +148,6 @@ static_library("browser") {
     "password_feature_manager.h",
     "password_feature_manager_impl.cc",
     "password_feature_manager_impl.h",
-    "password_form.h",
     "password_form_filling.cc",
     "password_form_filling.h",
     "password_form_manager.cc",
@@ -406,6 +405,17 @@ source_set("csv_unittests") {
   ]
 }
 
+# PasswordForm is an extremely common struct used by many sub-components and
+# sub-directories. Having its own target makes it possible to break up several
+# cyclic dependencies.
+source_set("password_form") {
+  sources = [
+    "password_form.h",
+    "password_form_forward.h",
+  ]
+  deps = [ "//components/autofill/core/common" ]
+}
+
 static_library("password_generator") {
   sources = [
     "generation/password_generator.cc",

components/password_manager/core/browser/password_form_forward.h

+// Copyright 2020 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.
+
+#ifndef COMPONENTS_PASSWORD_MANAGER_CORE_BROWSER_PASSWORD_FORM_FORWARD_H_
+#define COMPONENTS_PASSWORD_MANAGER_CORE_BROWSER_PASSWORD_FORM_FORWARD_H_
+
+// While `password_manager::PasswordForm` is just an alias to
+// `autofill::PasswordForm` it is rather awkward to construct a forward
+// declaration for it, since a naive solution such as
+// namespace password_manager { struct PasswordForm; } would break the build.
+// This file aims to make this easier, and classes merely interested in a
+// forward declaration can simply #include this header.
+//
+// TODO(crbug.com/1067347): Remove this file once password_manager::PasswordForm
+// is a real class, and a regular forward declaration does work.
+namespace autofill {
+struct PasswordForm;
+}
+
+namespace password_manager {
+using PasswordForm = autofill::PasswordForm;
+}
+
+#endif  // COMPONENTS_PASSWORD_MANAGER_CORE_BROWSER_PASSWORD_FORM_FORWARD_H_