Refactor //ios/web_view sources into its own source_set target

- This avoids rebuilding the same sources for the framework and test.
- Created a stub implementation of ios_web_view::InitializeGlobalState
  to avoid multiple AtExitManagers in unit tests.

Change-Id: Ia1a839f2be06d8a9e2974d2e8edb9cf399e849cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2121035
Commit-Queue: John Wu <jzw@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Hiroshi Ichikawa <ichikawa@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756028}

ios/web_view/internal/web_view_global_state_util.mm

@@ -18,11 +18,6 @@
 namespace ios_web_view {
 
 void InitializeGlobalState() {
-  // Do not perform global state initialization in an unit test environment.
-  // 1. Not needed when unit testing.
-  // 2. The globals below will try to create other already created globals like
-  //    AtExitManagers. This causes DCHECKs and prevents tests from completing.
-#if !defined(UNIT_TEST)
   static std::unique_ptr<ios_web_view::WebViewWebClient> web_client;
   static std::unique_ptr<ios_web_view::WebViewWebMainDelegate>
       web_main_delegate;
@@ -49,7 +44,6 @@ void InitializeGlobalState() {
                   web_client.reset();
                 }];
   });
-#endif  // defined(UNIT_TEST)
 }
 
 }  // namespace ios_web_view

ios/web_view/internal/web_view_global_state_util_stub.mm

+// 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.
+
+#include "ios/web_view/internal/web_view_global_state_util.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace ios_web_view {
+
+void InitializeGlobalState() {
+  // Do not perform global state initialization in an unit test environment.
+  // It's not needed and also avoids the issue of multiple AtExitManagers.
+}
+
+}  // namespace ios_web_view