Fix trailing whitespace test.

And write the test better to avoid overzealous editor plugins :)

TBR=eakuefner@chromium.org, nodir@chromium.org, vadimsh@chromium.org

Bug: 825290,825174
Change-Id: I0541d4d70bcb256c24cb659bae256fa0aacb6806
Reviewed-on: https://chromium-review.googlesource.com/979116
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>

tests/gclient_eval_unittest.py

@@ -25,7 +25,7 @@ vars = {
      # Some comment with bad indentation
      'dep_2_rev': '1ced',
  # Some more comments with bad indentation
-   # and trailing whitespaces
+   # and trailing whitespaces  """ + """
    'dep_3_rev': '5p1e5',
 }