[cr tool] Fixing import problems

tools/cr/cr/plugin.py

Index: tools/cr/cr/plugin.py
diff --git a/tools/cr/cr/plugin.py b/tools/cr/cr/plugin.py
index 05a02cb1b1924a88b6040474be366288efbe2cab..eccd86954aa44abed7249fe8b5677d5b69b78583 100644
--- a/tools/cr/cr/plugin.py
+++ b/tools/cr/cr/plugin.py
@@ -182,6 +182,10 @@ class Plugin(cr.loader.AutoExport):
         getattr(self, config_root.property_name).enabled = False
 
   @classmethod
+  def ClassInit(cls):
+    pass
+
+  @classmethod
   def GetInstance(cls):
     """Gets an instance of this plugin.
 
@@ -193,6 +197,8 @@ class Plugin(cr.loader.AutoExport):
     """
     plugin = _plugins.get(cls, None)
     if plugin is None:
+      # Run delayed class initialization
+      cls.ClassInit()
       # Build a new instance of cls, and register it as the main instance.
       plugin = cls()
       _plugins[cls] = plugin