Bug 1442378 - part 5 - make multiple occurrences of the same file fatal; r=jmaher

We shouldn't really have this problem, and shouting about it early will
make sure that we address issues like multiple instances of omni.ja,
rather than not recording information that we should have been.

testing/mozharness/mozharness/mozilla/building/buildbase.py

@@ -1612,13 +1612,10 @@ or run without that action (ie: --no-{action})"
                             if containing_dir == 'browser':
                                 name = 'browser-omni.ja'
                         if name in subtests:
-                            # File seen twice in same archive;
-                            # ignore to avoid confusion.
-                            subtests[name] = None
-                        else:
+                            self.fatal('should not see %s (%s) multiple times!'
+                                       % (name, path))
                         subtests[name] = size
                 for name in subtests:
-                    if subtests[name] is not None:
                     self.info('Size of %s: %s bytes' % (name,
                                                         subtests[name]))
                     size_measurements.append(