Build retrace when running app dumps

Currently the bot can't retrace the failures on the dump bot and
therefore also eat the non retraced stack!

Change-Id: I5f92de9e17601265718e09691cd773da84d211ad
diff --git a/tools/run_on_app_dump.py b/tools/run_on_app_dump.py
index 88c758d..f71a314 100755
--- a/tools/run_on_app_dump.py
+++ b/tools/run_on_app_dump.py
@@ -1107,7 +1107,7 @@
           quiet=options.quiet)
     elif options.version == 'main':
       if not (options.no_build or options.golem):
-        gradle.RunGradle(['r8', '-Pno_internal'])
+        gradle.RunGradle(['R8Retrace', 'r8', '-Pno_internal'])
         build_r8lib = False
         for shrinker in options.shrinker:
           if is_minified_r8(shrinker):