Use ATTRIBUTE_UNUSED more.

Use it in lieu of UNUSED(), which had some incorrect uses.

Change-Id: If247dce58b72056f6eea84968e7196f0b5bef4da
diff --git a/runtime/jni_env_ext.cc b/runtime/jni_env_ext.cc
index 4104d7a..dab1040 100644
--- a/runtime/jni_env_ext.cc
+++ b/runtime/jni_env_ext.cc
@@ -93,8 +93,7 @@
   monitors.Dump(os);
 }
 
-void JNIEnvExt::PushFrame(int capacity) {
-  UNUSED(capacity);  // cpplint gets confused with (int) and thinks its a cast.
+void JNIEnvExt::PushFrame(int capacity ATTRIBUTE_UNUSED) {
   // TODO: take 'capacity' into account.
   stacked_local_ref_cookies.push_back(local_ref_cookie);
   local_ref_cookie = locals.GetSegmentState();