Bump oat version number and add OatHeaderSizeCheck test

Change-Id: I07d189adc5071bcf45b3dad0246d7082852159ae
diff --git a/src/oat_test.cc b/src/oat_test.cc
index 3e92a15..dae61bb 100644
--- a/src/oat_test.cc
+++ b/src/oat_test.cc
@@ -119,4 +119,11 @@
   }
 }
 
+TEST_F(OatTest, OatHeaderSizeCheck) {
+  // If this test is failing and you have to update these constants,
+  // it is time to update OatHeader::kOatVersion
+  EXPECT_EQ(32U, sizeof(OatHeader));
+  EXPECT_EQ(32U, sizeof(OatMethodOffsets));
+}
+
 }  // namespace art