[groovy] add isThisExpression and update isSuperExpression

plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/util/psiUtil.kt

@@ -1,17 +1,5 @@
 /*
- * Copyright 2000-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
  */
 package org.jetbrains.plugins.groovy.lang.psi.util
 
@@ -51,6 +39,9 @@ fun modifierListMayBeEmpty(owner: PsiElement?): Boolean = when (owner) {
 }
 
 fun GrExpression?.isSuperExpression(): Boolean {
-  val referenceExpression = this as? GrReferenceExpression
-  return referenceExpression?.referenceNameElement?.node?.elementType == GroovyTokenTypes.kSUPER
+  return this is GrReferenceExpression && referenceNameElement?.node?.elementType === GroovyTokenTypes.kSUPER
+}
+
+fun GrExpression?.isThisExpression(): Boolean {
+  return this is GrReferenceExpression && referenceNameElement?.node?.elementType === GroovyTokenTypes.kTHIS
 }