Add --debug-agent flag to run_on_app.py

Change-Id: If80542ccd52d7c5f4a307f016efe923938dec945
diff --git a/tools/run_on_app.py b/tools/run_on_app.py
index 07de70c..1687797 100755
--- a/tools/run_on_app.py
+++ b/tools/run_on_app.py
@@ -109,6 +109,10 @@
                     help='Run without debug asserts.',
                     default=False,
                     action='store_true')
+  result.add_option('--debug-agent',
+                    help='Run with debug agent.',
+                    default=False,
+                    action='store_true')
   result.add_option('--version',
                     help='The version of the app to run')
   result.add_option('-k',
@@ -519,6 +523,12 @@
     if 'allow-type-errors' in values:
       extra_args.append('-Dcom.android.tools.r8.allowTypeErrors=1')
 
+  if options.debug_agent:
+    if not options.compiler_build == 'full':
+      print('WARNING: Running debugging agent on r8lib is questionable...')
+    extra_args.append(
+      '-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=*:5005')
+
   if not options.no_libraries:
     for lib in libraries:
       args.extend(['--lib', lib])