Fix python3 using decimal for Xmx

Bug: 177898307
Change-Id: I2ee934eb1f654d86cb0e0902fcffd5b4f43708f2
diff --git a/tools/run_on_app.py b/tools/run_on_app.py
index 1e3d292..749aee6 100755
--- a/tools/run_on_app.py
+++ b/tools/run_on_app.py
@@ -275,9 +275,9 @@
   else:
     working = 1024 * 8
   exit_code = 0
-  range = options.find_min_xmx_range_size
+  range = int(options.find_min_xmx_range_size)
   while working - not_working > range:
-    next_candidate = working - ((working - not_working)/2)
+    next_candidate = int(working - ((working - not_working)/2))
     print('working: %s, non_working: %s, next_candidate: %s' %
           (working, not_working, next_candidate))
     extra_args = ['-Xmx%sM' % next_candidate]