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

ios/web/public/web_state/page_viewport_state_unittest.mm

 // Copyright 2016 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/web_state/page_viewport_state.h"
 
 #include "base/macros.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 // Verifies viewport length construction for "device-width" and "device-height".
 TEST(ViewportLengthTest, DeviceDimension) {
   ViewportLength device_width(@"device-width");
   EXPECT_TRUE(device_width.use_device_length());
   EXPECT_TRUE(isnan(device_width.value()));
   ViewportLength device_height(@"device-height");
   EXPECT_TRUE(device_height.use_device_length());
   EXPECT_TRUE(isnan(device_height.value()));
@@ skipping 44 matching lines @@
   EXPECT_TRUE(state.user_scalable());
   state = PageViewportState(@"user-scalable=1");
   EXPECT_TRUE(state.user_scalable());
   state = PageViewportState(@"user-scalable=no");
   EXPECT_FALSE(state.user_scalable());
   state = PageViewportState(@"user-scalable=0");
   EXPECT_FALSE(state.user_scalable());
 }
 
 }  // namespace web