AAPT2: Add round qualifer support

Change-Id: Id5a1331198e01be7ca4d87b8833900e51f82ece5
diff --git a/tools/aapt2/SdkConstants.h b/tools/aapt2/SdkConstants.h
index 803da03..282ed9a 100644
--- a/tools/aapt2/SdkConstants.h
+++ b/tools/aapt2/SdkConstants.h
@@ -42,6 +42,7 @@
     SDK_KITKAT_WATCH = 20,
     SDK_LOLLIPOP = 21,
     SDK_LOLLIPOP_MR1 = 22,
+    SDK_MARSHMALLOW = 23,
 };
 
 size_t findAttributeSdkLevel(ResourceId id);