Use ATTRIBUTE_UNUSED more.

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

Change-Id: If247dce58b72056f6eea84968e7196f0b5bef4da
diff --git a/runtime/gc/task_processor_test.cc b/runtime/gc/task_processor_test.cc
index 2c44da2..f1d26d9 100644
--- a/runtime/gc/task_processor_test.cc
+++ b/runtime/gc/task_processor_test.cc
@@ -105,8 +105,7 @@
   TestOrderTask(uint64_t expected_time, size_t expected_counter, size_t* counter)
      : HeapTask(expected_time), expected_counter_(expected_counter), counter_(counter) {
   }
-  virtual void Run(Thread* thread) OVERRIDE {
-    UNUSED(thread);  // Fix cppling bug.
+  virtual void Run(Thread* thread ATTRIBUTE_UNUSED) OVERRIDE {
     ASSERT_EQ(*counter_, expected_counter_);
     ++*counter_;
   }