object declarations need trait methods to be generated too (KT-2399)

compiler/testData/codegen/regressions/kt2399.kt

@@ -0,0 +1,43 @@
+import java.util.Collection
+import java.util.ArrayList
+
+class JsonObject {
+}
+
+class JsonArray {
+}
+
+class ProjectInfo {
+    public fun toString(): String = "OK"
+}
+
+public trait Parser<in IN: Any, out OUT: Any> {
+    public fun parse(source: IN): OUT
+}
+
+public trait MultiParser<in IN: Any, out OUT: Any> {
+    public fun parse(source: IN): Collection<OUT>
+}
+
+public trait JsonParser<T: Any>: Parser<JsonObject, T>, MultiParser<JsonArray, T> {
+    public override fun parse(source: JsonArray): Collection<T> {
+        return ArrayList<T>()
+    }
+}
+
+public abstract class ProjectInfoJsonParser(): JsonParser<ProjectInfo> {
+    public override fun parse(source: JsonObject): ProjectInfo {
+        return ProjectInfo()
+    }
+}
+
+class ProjectApiContext {
+    public val projectInfoJsonParser: ProjectInfoJsonParser = object : ProjectInfoJsonParser(){
+    }
+}
+
+fun box(): String {
+    val context = ProjectApiContext()
+    val array = context.projectInfoJsonParser.parse(JsonArray())
+    return if (array != null) "OK" else "fail"
+}