[ObjC ARC] Converts ios/web:ios_web_web_state_unittests to ARC.

ios/web/web_state/page_display_state_unittest.mm

 // Copyright 2017 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.
 
 #import "ios/web/public/web_state/page_display_state.h"
 
-#import "base/mac/scoped_nsobject.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 #define EXPECT_NAN(value) EXPECT_NE(value, value)
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 // Tests that the empty constructor creates an invalid PageDisplayState with all
 // NAN values.
 TEST(PageDisplayStateTest, EmptyConstructor) {
   web::PageDisplayState state;
   EXPECT_NAN(state.scroll_state().offset_x());
   EXPECT_NAN(state.scroll_state().offset_y());
   EXPECT_NAN(state.zoom_state().minimum_zoom_scale());
   EXPECT_NAN(state.zoom_state().maximum_zoom_scale());
   EXPECT_NAN(state.zoom_state().zoom_scale());
   EXPECT_FALSE(state.IsValid());
@@ skipping 29 matching lines @@
   EXPECT_EQ(1.0, state.scroll_state().offset_y());
   EXPECT_EQ(1.0, state.zoom_state().minimum_zoom_scale());
   EXPECT_EQ(5.0, state.zoom_state().maximum_zoom_scale());
   EXPECT_EQ(1.0, state.zoom_state().zoom_scale());
   EXPECT_TRUE(state.IsValid());
 }
 
 // Tests converting between a PageDisplayState, its serialization, and back.
 TEST(PageDisplayStateTest, Serialization) {
   web::PageDisplayState state(0.0, 1.0, 1.0, 5.0, 1.0);
-  base::scoped_nsobject<NSDictionary> serialization(
-      [state.GetSerialization() retain]);
+  NSDictionary* serialization = state.GetSerialization();

[Eugene But (OOO till 7-30), 2017/06/14 13:34:02]

Optional nit: consider dropping |serialization| local if it works.

[marq (ping after 24h), 2017/06/14 14:18:23]

Done.

   web::PageDisplayState new_state(serialization);
   EXPECT_EQ(state, new_state);
 }