Create the harness and shell of update_test_expectations

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py
new file mode 100644
index 0000000000000000000000000000000000000000..101cd9bcd9d166e6ac8c3e28f8e5b8962b03e0c6
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+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_test_expectations.py
@@ -0,0 +1,89 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Updates TestExpectations based on results in builder bots.
+
+Scans the TestExpectations file and uses results from actual builder bots runs
+to remove tests that are marked as flaky but don't fail in the specified way.
+
+E.g. If a test has this expectation:
+    bug(test) fast/test.html [ Failure Pass ]
+
+And all the runs on builders have passed the line will be removed.
+
+Additionally, the runs don't all have to be Passing to remove the line;
+as long as the non-Passing results are of a type not specified in the
+expectation this line will be removed. For example, if this is the
+expectation:
+
+    bug(test) fast/test.html [ Crash Pass ]
+
+But the results on the builders show only Passes and Timeouts, the line
+will be removed since there's no Crash results.
+"""
+
+import argparse
+import logging
+
+from webkitpy.layout_tests.models.test_expectations import TestExpectations
+
+_log = logging.getLogger(__name__)
+
+
+def main(host, bot_test_expectations_factory, argv):
+    parser = argparse.ArgumentParser(epilog=__doc__, formatter_class=argparse.RawTextHelpFormatter)
+    parser.parse_args(argv)
+
+    port = host.port_factory.get()
+
+    logging.basicConfig(level=logging.INFO, format="%(message)s")
+
+    expectations_file = port.path_to_generic_test_expectations_file()
+    if not host.filesystem.isfile(expectations_file):
+        _log.warn("Didn't find generic expectations file at: " + expectations_file)
+        return 1
+
+    remove_flakes_o_matic = RemoveFlakesOMatic(host,
+                                               port,
+                                               bot_test_expectations_factory)
+
+    test_expectations = remove_flakes_o_matic.get_updated_test_expectations()
+
+    remove_flakes_o_matic.write_test_expectations(test_expectations,
+                                                  expectations_file)
+    return 0
+
+
+class RemoveFlakesOMatic(object):
+    def __init__(self, host, port, bot_test_expectations_factory):
+        self._host = host
+        self._port = port
+        self._expectations_factory = bot_test_expectations_factory
+        self.builder_results_by_path = {}
+
+    def get_updated_test_expectations(self):
+        """Filters out passing lines from TestExpectations file.
+
+        Reads the current TestExpectations file and, using results from the
+        build bots, removes lines that are passing. That is, removes lines that
+        were not needed to keep the bots green.
+
+        Returns:
+            A TestExpectations object with the passing lines filtered out.
+        """
+        test_expectations = TestExpectations(self._port, include_overrides=False).expectations()
+        # TODO: Filter the expectations based on results.
+        return test_expectations
+
+    def write_test_expectations(self, test_expectations, test_expectations_file):
+        """Writes the given TestExpectations object to the filesystem.
+
+        Args:
+            test_expectations: The TestExpectations object to write.
+            test_expectations_file: The full file path of the Blink
+                TestExpectations file. This file will be overwritten.
+        """
+        self._host.filesystem.write_text_file(
+            test_expectations_file,
+            TestExpectations.list_to_string(test_expectations, reconstitute_only_these=[]))