make test.py more reselient to flakyness in xvfb-run + DumpRenderTree

tools/testing/test_case.py

Index: tools/testing/test_case.py
diff --git a/tools/testing/test_case.py b/tools/testing/test_case.py
index aa219594156f1a5274b64110c39cb8baa7394ee4..0f3c4458c8976b21705306f2c850d768998c9be0 100644
--- a/tools/testing/test_case.py
+++ b/tools/testing/test_case.py
@@ -124,6 +124,12 @@ class BrowserTestCase(StandardTestCase):
     # the output does.
     if self.run_arch.HasFailed(test_output.output.stdout):
       test_output.output.exit_code = 1
+      # DumpRenderTree is sometimes flaky in xvfb-run, try again in that case.
+      if (self.run_arch.WasFlakyDrt(test_output.output.stderr)):
+        print "\nFlaky Gtw-WARNING error found, trying again..."
+        test_output = self.RunCommand(command)
+        if self.run_arch.HasFailed(test_output.output.stdout):
+          test_output.output.exit_code = 1
 
     return test_output