V8: Add temporary output to slave-distribution method.

scripts/master/master_utils.py

Index: scripts/master/master_utils.py
diff --git a/scripts/master/master_utils.py b/scripts/master/master_utils.py
index f0f5e1bb14e5d36185f345130b0519312e402447..d9907482fe1e64b636d9f4725ff7c2e686a3aba3 100644
--- a/scripts/master/master_utils.py
+++ b/scripts/master/master_utils.py
@@ -704,10 +704,18 @@ class PreferredBuilderNextSlaveFuncNG(object):
       # one group will be chosen arbitrarily, the actual slave will be chosen
       # randomly.
       key = prefs.most_common()[0][0]
-    return self._choice(
+    result = self._choice(
         [s for s in slave_builders
          if s.slave.properties.getProperty('preferred_builder') == key])
 
+    log.msg('Assigning slave to %s. Preferred: %s. Chose %s.' % (
+        builder.name,
+        [s.slave.properties.getProperty('preferred_builder')
+         for s in slave_builders],
+        result))
+
+    return result
+
 
 def SetMasterProcessName():
   """Sets the name of this process to the name of the master.  Linux only."""