[ARC] Converts part of ios/web/public to ARC.

ios/web/public/web_state/page_display_state.mm

 // Copyright 2015 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/public/web_state/page_display_state.h"
 
 #include <cmath>
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 namespace {
 // Returns true if:
 // - both |value1| and |value2| are NAN, or
 // - |value1| and |value2| are equal non-NAN values.
 inline bool StateValuesAreEqual(double value1, double value2) {
   return std::isnan(value1) ? std::isnan(value2) : value1 == value2;
 }
 }  // namespace
@@ skipping 80 matching lines @@
 bool PageDisplayState::operator==(const PageDisplayState& other) const {
   return scroll_state_ == other.scroll_state_ &&
          zoom_state_ == other.zoom_state_;
 }
 
 bool PageDisplayState::operator!=(const PageDisplayState& other) const {
   return !(*this == other);
 }
 
 }  // namespace web