Ensure apps can't directly access the dnsresolver service.

Test: test-only change
Change-Id: I142a13f4ab19ff000e2bd89a8de3c293004723ff

tests/cts/net/src/android/net/cts/DnsResolverTest.java

@@ -860,4 +860,9 @@ public class DnsResolverTest {
             assertEquals(DnsResolver.ERROR_SYSTEM, e.code);
         }
     }
+
+    @Test
+    public void testNoRawBinderAccess() {
+        assertNull(mContext.getSystemService("dnsresolver"));
+    }
 }