Ensure apps can't directly access the dnsresolver service.

Test: test-only change
Change-Id: I142a13f4ab19ff000e2bd89a8de3c293004723ff
diff --git a/tests/cts/net/src/android/net/cts/DnsResolverTest.java b/tests/cts/net/src/android/net/cts/DnsResolverTest.java
index 308aead..9ff0f2f 100644
--- a/tests/cts/net/src/android/net/cts/DnsResolverTest.java
+++ b/tests/cts/net/src/android/net/cts/DnsResolverTest.java
@@ -860,4 +860,9 @@
             assertEquals(DnsResolver.ERROR_SYSTEM, e.code);
         }
     }
+
+    @Test
+    public void testNoRawBinderAccess() {
+        assertNull(mContext.getSystemService("dnsresolver"));
+    }
 }