[test] Deprecate test data download for most test suites

tools/testrunner/local/testsuite.py

Index: tools/testrunner/local/testsuite.py
diff --git a/tools/testrunner/local/testsuite.py b/tools/testrunner/local/testsuite.py
index f8ccc0c4fa8f448e03a5df6fd844188b95780181..c24dcf8d43c609873e5b315cc80de33d9b8cf7dd 100644
--- a/tools/testrunner/local/testsuite.py
+++ b/tools/testrunner/local/testsuite.py
@@ -125,6 +125,14 @@ class TestSuite(object):
     """
     return self._VariantGeneratorFactory()(self, set(variants))
 
+  def PrepareSources(self):
+    """Called once before multiprocessing for doing file-system operations.
+
+    This should not access the network. For network access use the method
+    below.
+    """
+    pass
+
   def DownloadData(self):
     pass