Migrate WTF::HashMap::get() to ::at()

third_party/WebKit/Source/core/css/PropertyRegistry.cpp

 // 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.
 
 #include "core/css/PropertyRegistry.h"
 
 namespace blink {
 
 void PropertyRegistry::registerProperty(
     const AtomicString& name,
     const CSSSyntaxDescriptor& syntax,
     bool inherits,
     const CSSValue* initial,
     PassRefPtr<CSSVariableData> initialVariableData,
     CSSInterpolationTypes cssInterpolationTypes) {
   DCHECK(!registration(name));
   m_registrations.set(
       name, new PropertyRegistration(syntax, inherits, initial,
                                      std::move(initialVariableData),
                                      std::move(cssInterpolationTypes)));
 }
 
 const PropertyRegistration* PropertyRegistry::registration(
     const AtomicString& name) const {
-  return m_registrations.get(name);
+  return m_registrations.at(name);
 }
 
 }  // namespace blink