Refactor atomic integer.

Refactored atomic integer to be similar to c++11 std::atomic<int>.

Removed jdwp serial lock and reverted lock level name change from
https://googleplex-android-review.googlesource.com/#/c/327297/

Change-Id: I2229f30c4d5762a0e8c72697d6aca4683750af35
diff --git a/runtime/thread_pool_test.cc b/runtime/thread_pool_test.cc
index e2a32f5..4717ce7 100644
--- a/runtime/thread_pool_test.cc
+++ b/runtime/thread_pool_test.cc
@@ -95,7 +95,7 @@
   EXPECT_EQ(0, bad_count);
   // Allow tasks to finish up and delete themselves.
   thread_pool.StartWorkers(self);
-  while (count.get() != num_tasks && bad_count.get() != 1) {
+  while (count.load() != num_tasks && bad_count.load() != 1) {
     usleep(200);
   }
   thread_pool.StopWorkers(self);