Fix ART test depending on libcore internals.

The test was accessing an internal field which is now blacklisted.
This CL changes it to use another's classes instance field that
is part of the SDK API.

Test: art/test/testrunner/testrunner.py -b --host -t 918
Change-Id: I8f825c51acb5ab646e88cc94b27d95496e2d6788
diff --git a/test/918-fields/expected.txt b/test/918-fields/expected.txt
index af78615..0114ccc 100644
--- a/test/918-fields/expected.txt
+++ b/test/918-fields/expected.txt
@@ -2,9 +2,9 @@
 class java.lang.Math
 25
 false
-[value, I, null]
-class java.lang.Integer
-18
+[bytesTransferred, I, null]
+class java.io.InterruptedIOException
+1
 false
 [this$0, Lart/Test918;, null]
 class art.Test918$Foo
@@ -18,3 +18,7 @@
 class art.Test918$Generics
 0
 false
+[privateValue, I, null]
+class art.Test918$Generics
+2
+false
diff --git a/test/918-fields/src/art/Test918.java b/test/918-fields/src/art/Test918.java
index ca23c03..5328b0b 100644
--- a/test/918-fields/src/art/Test918.java
+++ b/test/918-fields/src/art/Test918.java
@@ -16,6 +16,7 @@
 
 package art;
 
+import java.io.InterruptedIOException;
 import java.lang.reflect.Field;
 import java.util.Arrays;
 
@@ -26,10 +27,11 @@
 
   public static void doTest() throws Exception {
     testField(Math.class, "PI");
-    testField(Integer.class, "value");
+    testField(InterruptedIOException.class, "bytesTransferred");
     testField(Foo.class, "this$0");
     testField(Bar.class, "VAL");
     testField(Generics.class, "generics");
+    testField(Generics.class, "privateValue");
   }
 
   private static void testField(Class<?> base, String fieldName)
@@ -71,5 +73,6 @@
 
   private static class Generics<T> {
     T generics;
+    private int privateValue = 42;
   }
 }