Minor. Use ArrayList instead of LinkedHashSet

Looks like there's no duplicates anyway

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedMemberScope.kt

@@ -30,7 +30,7 @@ import org.jetbrains.kotlin.serialization.ProtoBuf
 import org.jetbrains.kotlin.serialization.deserialization.DeserializationContext
 import org.jetbrains.kotlin.storage.getValue
 import org.jetbrains.kotlin.utils.Printer
-import org.jetbrains.kotlin.utils.toReadOnlyList
+import org.jetbrains.kotlin.utils.compactIfPossible
 import java.util.*
 
 abstract class DeserializedMemberScope protected constructor(
@@ -84,10 +84,10 @@ abstract class DeserializedMemberScope protected constructor(
     ): Collection<D> {
         val protos = protosByName[name].orEmpty()
 
-        val descriptors = protos.mapTo(linkedSetOf(), factory)
+        val descriptors = protos.mapTo(arrayListOf(), factory)
 
         computeNonDeclared(descriptors)
-        return descriptors.toReadOnlyList()
+        return descriptors.compactIfPossible()
     }
 
     protected open fun computeNonDeclaredFunctions(name: Name, functions: MutableCollection<SimpleFunctionDescriptor>) {
@@ -126,7 +126,7 @@ abstract class DeserializedMemberScope protected constructor(
     ): Collection<DeclarationDescriptor> {
         //NOTE: descriptors should be in the same order they were serialized in
         // see MemberComparator
-        val result = LinkedHashSet<DeclarationDescriptor>(0)
+        val result = ArrayList<DeclarationDescriptor>(0)
 
         if (kindFilter.acceptsKinds(DescriptorKindFilter.SINGLETON_CLASSIFIERS_MASK)) {
             addEnumEntryDescriptors(result, nameFilter)
@@ -140,7 +140,7 @@ abstract class DeserializedMemberScope protected constructor(
             addClassifierDescriptors(result, nameFilter)
         }
 
-        return result.toReadOnlyList()
+        return result.compactIfPossible()
     }
 
     private fun addFunctionsAndProperties(

core/util.runtime/src/org/jetbrains/kotlin/utils/collections.kt

@@ -84,6 +84,13 @@ fun <T> Collection<T>.toReadOnlyList(): List<T> =
             else -> ArrayList(this)
         }
 
+fun <T> ArrayList<T>.compactIfPossible(): List<T> =
+        when (size) {
+            0 -> emptyList()
+            1 -> listOf(first())
+            else -> apply(ArrayList<T>::trimToSize)
+        }
+
 fun <T: Any> T?.singletonOrEmptyList(): List<T> =
         if (this != null) listOf(this) else emptyList()