tools/metrics/rappor/pretty_print_test.py doesn't pass at TOT in Chromium.

I think it's been broken for a while. Output:

EEEE
======================================================================
ERROR: testInvalidTypes (__main__.ActionXmlTest)
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Traceback (most recent call last):
  File "./tools/metrics/rappor/pretty_print_test.py", line 116, in testInvalidTypes
    self.assertFalse(pretty_print.GetInvalidTypeErrors(
AttributeError: 'module' object has no attribute 'GetInvalidTypeErrors'

======================================================================
ERROR: testIsPretty (__main__.ActionXmlTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./tools/metrics/rappor/pretty_print_test.py", line 99, in testIsPretty
    result = pretty_print.UpdateXML(PRETTY_XML)
AttributeError: 'module' object has no attribute 'UpdateXML'

======================================================================
ERROR: testMissingOwners (__main__.ActionXmlTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./tools/metrics/rappor/pretty_print_test.py", line 110, in testMissingOwners
    self.assertFalse(pretty_print.GetMissingOwnerErrors([BASIC_METRIC]))
AttributeError: 'module' object has no attribute 'GetMissingOwnerErrors'

======================================================================
ERROR: testParsing (__main__.ActionXmlTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./tools/metrics/rappor/pretty_print_test.py", line 103, in testParsing
    comments, config = pretty_print.RAPPOR_XML_TYPE.Parse(PRETTY_XML)
AttributeError: 'module' object has no attribute 'RAPPOR_XML_TYPE'

----------------------------------------------------------------------
Ran 4 tests in 0.000s

FAILED (errors=4)


We should fix it and when it's fixed, it can be added to the metrics_python_tests test suite I added under https://bugs.chromium.org/p/chromium/issues/detail?id=757504