Make debugger not fail with webpages_playback script and multiple skp files

The debugger accepts either a single skp or a directory as a parameter.
The webpages_playback script used to pass multiple files using a '*'
glob.

Review URL: https://codereview.chromium.org/775073002
diff --git a/tools/skp/webpages_playback.py b/tools/skp/webpages_playback.py
index d5054bf..422edbc 100644
--- a/tools/skp/webpages_playback.py
+++ b/tools/skp/webpages_playback.py
@@ -310,7 +310,7 @@
       if not self._non_interactive:
         print '\n\n=======Running debugger======='
         os.system('%s %s' % (os.path.join(self._skia_tools, 'debugger'),
-                             os.path.join(self._local_skp_dir, '*')))
+                             self._local_skp_dir))
 
     print '\n\n'