Bug 1442378 - part 3 - factor out common code for zipfiles vs. tarfiles; r=jmaher

The zipfile and tarfiles paths for finding interesting files in the
installer have duplicated code.  We can eliminate this duplicated code
by factoring out a function to just get the paths and sizes for files
contained in the installer.  If we need to make changes to how paths are
processed, we now only have to make the change in a single place, and we
can add other kinds of installers easily in the future.

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

@@ -1586,35 +1586,30 @@ or run without that action (ie: --no-{action})"
         installer_size = 0
         size_measurements = []
 
+        def paths_with_sizes(installer):
+            if zipfile.is_zipfile(installer):
+                with zipfile.ZipFile(installer, 'r') as zf:
+                    for zi in zf.infolist():
+                        yield zi.filename, zi.file_size
+            elif tarfile.is_tarfile(installer):
+                with tarfile.open(installer, 'r:*') as tf:
+                    for ti in tf:
+                        yield ti.name, ti.size
+
         if os.path.exists(installer):
             installer_size = self.query_filesize(installer)
             self.info('Size of %s: %s bytes' % (packageName, installer_size))
             try:
                 subtests = {}
-                if zipfile.is_zipfile(installer):
-                    with zipfile.ZipFile(installer, 'r') as zf:
-                        for zi in zf.infolist():
-                            name = os.path.basename(zi.filename)
-                            size = zi.file_size
-                            if name in interests:
-                                if name in subtests:
-                                    # File seen twice in same archive;
-                                    # ignore to avoid confusion.
-                                    subtests[name] = None
-                                else:
-                                    subtests[name] = size
-                elif tarfile.is_tarfile(installer):
-                    with tarfile.open(installer, 'r:*') as tf:
-                        for ti in tf:
-                            name = os.path.basename(ti.name)
-                            size = ti.size
-                            if name in interests:
-                                if name in subtests:
-                                    # File seen twice in same archive;
-                                    # ignore to avoid confusion.
-                                    subtests[name] = None
-                                else:
-                                    subtests[name] = size
+                for path, size in paths_with_sizes(installer):
+                    name = os.path.basename(path)
+                    if name in interests:
+                        if name in subtests:
+                            # File seen twice in same archive;
+                            # ignore to avoid confusion.
+                            subtests[name] = None
+                        else:
+                            subtests[name] = size
                 for name in subtests:
                     if subtests[name] is not None:
                         self.info('Size of %s: %s bytes' % (name,