Extract serialization of packageFqName extension to SerializerExtensionBase

compiler/serialization/src/org/jetbrains/kotlin/serialization/SerializerExtensionBase.kt

@@ -17,10 +17,14 @@
 package org.jetbrains.kotlin.serialization
 
 import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.resolve.constants.NullValue
 import org.jetbrains.kotlin.types.KotlinType
 
-open class KotlinSerializerExtensionBase(private val protocol: SerializerExtensionProtocol) : SerializerExtension() {
+open class KotlinSerializerExtensionBase(
+        private val protocol: SerializerExtensionProtocol,
+        private val packageFqName: FqName
+) : SerializerExtension() {
     override val stringTable = StringTableImpl()
 
     override fun serializeClass(descriptor: ClassDescriptor, proto: ProtoBuf.Class.Builder) {
@@ -29,6 +33,10 @@ open class KotlinSerializerExtensionBase(private val protocol: SerializerExtensi
         }
     }
 
+    override fun serializePackage(proto: ProtoBuf.Package.Builder) {
+        proto.setExtension(protocol.packageFqName, stringTable.getPackageFqNameIndex(packageFqName))
+    }
+
     override fun serializeConstructor(descriptor: ConstructorDescriptor, proto: ProtoBuf.Constructor.Builder) {
         for (annotation in descriptor.annotations) {
             proto.addExtension(protocol.constructorAnnotation, annotationSerializer.serializeAnnotation(annotation))