odrefresh: re-enable OdrFsUtilsTest.GetUsedSpace

Use stat() in test for size in blocks rather than rounding up the
written file size to integral number of 512-byte blocks.

Bug: 186730164
Test: atest art_odrefresh_tests
Test: atest --host art_odrefresh_tests
Change-Id: Ic0b3421451f9f8049b30d11ec73761e6871034b8
diff --git a/odrefresh/odr_fs_utils_test.cc b/odrefresh/odr_fs_utils_test.cc
index 6c43265..42912d3 100644
--- a/odrefresh/odr_fs_utils_test.cc
+++ b/odrefresh/odr_fs_utils_test.cc
@@ -118,7 +118,7 @@
   }
 }
 
-TEST_F(OdrFsUtilsTest, DISABLED_GetUsedSpace) {
+TEST_F(OdrFsUtilsTest, GetUsedSpace) {
   static constexpr size_t kFirstFileBytes = 1;
   static constexpr size_t kSecondFileBytes = 16111;
   static constexpr size_t kBytesPerBlock = 512;
@@ -148,7 +148,8 @@
   for (size_t i = 1; i < 32768; i *= 17) {
     const std::string path = android::base::StringPrintf("%s/%zu", sub_dir_path.c_str(), i);
     ASSERT_TRUE(CreateFile(path.c_str(), i));
-    expected_bytes_used += RoundUp(i, sb.st_blocks * kBytesPerBlock);
+    ASSERT_EQ(0, stat(path.c_str(), &sb));
+    expected_bytes_used += sb.st_blocks * kBytesPerBlock;
     ASSERT_TRUE(GetUsedSpace(scratch_dir.GetPath().c_str(), &bytes_used));
     ASSERT_EQ(expected_bytes_used, bytes_used);
   }