In rebaseline-cl: add option to only rebaseline tests changed in the CL.

third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl.py b/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl.py
index ab839fc630c28336e1e45505af962364696d24ab..eb72502cd108ab61d7eb80ff25522db553858d9e 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl.py
@@ -12,11 +12,12 @@ import logging
 import optparse
 
 from webkitpy.common.checkout.scm.git import Git
-from webkitpy.common.net.rietveld import latest_try_jobs
+from webkitpy.common.net.buildbot import Build
+from webkitpy.common.net.rietveld import latest_try_jobs, changed_files
 from webkitpy.common.net.web import Web
+from webkitpy.common.webkit_finder import WebKitFinder
 from webkitpy.layout_tests.models.test_expectations import BASELINE_SUFFIX_LIST
 from webkitpy.tool.commands.rebaseline import AbstractParallelRebaselineCommand
-from webkitpy.tool.commands.rebaseline import Build
 
 
 _log = logging.getLogger(__name__)
@@ -24,7 +25,12 @@ _log = logging.getLogger(__name__)
 
 class RebaselineCL(AbstractParallelRebaselineCommand):
     name = "rebaseline-cl"
-    help_text = "Fetches new baselines for one CL, from layout test runs on try bots."
+    help_text = "Fetches new baselines for a CL from test runs on try bots."
+    long_help = ("By default, this command will check the latest try results "
+                 "and download new baselines for any tests that have been "
+                 "changed in the given CL that have failed and have new "
+                 "baselines. After downloading, the baselines for different "
+                 "platforms should be optimized (conslidated).")
     show_in_main_help = True
 
     def __init__(self):
@@ -35,6 +41,9 @@ class RebaselineCL(AbstractParallelRebaselineCommand):
             optparse.make_option(
                 '--dry-run', action='store_true', default=False,
                 help='Dry run mode; list actions that would be performed but do not do anything.'),
+            optparse.make_option(
+                '--only-changed-tests', action='store_true', default=False,
+                help='Only download new baselines for tests that are changed in the CL.'),
             self.no_optimize_option,
             self.results_directory_option,
         ])
@@ -51,7 +60,8 @@ class RebaselineCL(AbstractParallelRebaselineCommand):
             for test in args:
                 test_prefix_list[test] = {b: BASELINE_SUFFIX_LIST for b in builds}
         else:
-            test_prefix_list = self._test_prefix_list(issue_number)
+            test_prefix_list = self._test_prefix_list(
+                issue_number, only_changed_tests=options.only_changed_tests)
         self._log_test_prefix_list(test_prefix_list)
 
         if options.dry_run:
@@ -75,12 +85,28 @@ class RebaselineCL(AbstractParallelRebaselineCommand):
         # that this command can be called from outside of the repo.
         return Git(cwd=self._tool.filesystem.dirname(self._tool.path()))
 
-    def _test_prefix_list(self, issue_number):
-        """Returns a collection of test, builder and file extensions to get new baselines for."""
+    def _test_prefix_list(self, issue_number, only_changed_tests):
+        """Returns a collection of test, builder and file extensions to get new baselines for.
+
+        Args:
+            issue_number: The CL number of the change which needs new baselines.
+            only_changed_tests: Whether to only include baselines for tests that
+               are changed in this CL. If False, all new baselines for failing
+               tests will be downloaded, even for tests that were not modified.
+
+        Returns:
+            A dict containing information about which new baselines to download.
+        """
         builds_to_tests = self._builds_to_tests(issue_number)
+        if only_changed_tests:
+            files_in_cl = changed_files(issue_number, self.web)
+            finder = WebKitFinder(self._tool.filesystem)
+            tests_in_cl = [finder.layout_test_name(f) for f in files_in_cl]
         result = {}
         for build, tests in builds_to_tests.iteritems():
             for test in tests:
+                if only_changed_tests and test not in tests_in_cl:
+                    continue
                 if test not in result:
                     result[test] = {}
                 result[test][build] = BASELINE_SUFFIX_LIST
@@ -100,7 +126,7 @@ class RebaselineCL(AbstractParallelRebaselineCommand):
         return builds_to_tests
 
     def _try_bots(self):
-        """Retuns a collection of try bot builders to fetch results for."""
+        """Returns a collection of try bot builders to fetch results for."""
         return self._tool.builders.all_try_builder_names()
 
     def _unexpected_mismatch_results(self, try_job):