Fix profile-backoff usage message

Change-Id: Icccd7bbc0c7b6a088a00dfc7f8c52991ec87f544
diff --git a/runtime/parsed_options.cc b/runtime/parsed_options.cc
index f81c25f..750a291 100644
--- a/runtime/parsed_options.cc
+++ b/runtime/parsed_options.cc
@@ -790,7 +790,7 @@
   UsageMessage(stream, "  -Xprofile-period:integervalue\n");
   UsageMessage(stream, "  -Xprofile-duration:integervalue\n");
   UsageMessage(stream, "  -Xprofile-interval:integervalue\n");
-  UsageMessage(stream, "  -Xprofile-backoff:integervalue\n");
+  UsageMessage(stream, "  -Xprofile-backoff:doublevalue\n");
   UsageMessage(stream, "  -Xcompiler-option dex2oat-option\n");
   UsageMessage(stream, "  -Ximage-compiler-option dex2oat-option\n");
   UsageMessage(stream, "\n");