Remove base-* directories from gm expected/actual paths; just use platform names

buildbot/slave/skia_slave_scripts/run_decoding_tests.py

Index: buildbot/slave/skia_slave_scripts/run_decoding_tests.py
===================================================================
--- buildbot/slave/skia_slave_scripts/run_decoding_tests.py	(revision 10693)
+++ buildbot/slave/skia_slave_scripts/run_decoding_tests.py	(working copy)
@@ -12,10 +12,8 @@
   def _Run(self):
     cmd = ['-r', self._device_dirs.SKImageInDir(), '--noreencode']
 
-    # TODO(scroggo): Once we have expectations files with the new name,
-    # the expectations_name will use self._builder_name
-    if self._gm_image_subdir is not None:
-      expectations_name = self._gm_image_subdir + '.json'
+    if self._builder_name is not None:
+      expectations_name = self._builder_name + '.json'
 
       # Read expectations, which were downloaded/copied to the device.
       expectations_file = self._flavor_utils.DevicePathJoin(