ART: Add GetClassLoader

Add support for GetClassLoader. Add a test.

Bug: 31684578
Test: m test-art-host-run-test-912-classes
Change-Id: I629ec2a1f4843bc3b28e40111805e250be44d993
diff --git a/test/912-classes/expected.txt b/test/912-classes/expected.txt
index 9f5254c..3507a1a 100644
--- a/test/912-classes/expected.txt
+++ b/test/912-classes/expected.txt
@@ -39,3 +39,7 @@
 class Main$ClassA [interface Main$InfA]
 class Main$ClassB [interface Main$InfB]
 class Main$ClassC [interface Main$InfA, interface Main$InfC]
+class java.lang.String null
+class [Ljava.lang.String; null
+interface Main$InfA dalvik.system.PathClassLoader
+class $Proxy0 dalvik.system.PathClassLoader