[tools/vim] Only run PRESUBMIT unittests for changes that touch YCM config.

tools/vim/PRESUBMIT.py

Index: tools/vim/PRESUBMIT.py
diff --git a/tools/vim/PRESUBMIT.py b/tools/vim/PRESUBMIT.py
index 8b0e945be8e7acaa704c34763ebf399a5510041e..0456d37e86b253b1657275063c4ff16af79aadc6 100644
--- a/tools/vim/PRESUBMIT.py
+++ b/tools/vim/PRESUBMIT.py
@@ -8,5 +8,23 @@ Runs Python unit tests in /tools/vim/tests on upload.
 """
 
 def CheckChangeOnUpload(input_api, output_api):
-  return input_api.canned_checks.RunUnitTestsInDirectory(
-      input_api, output_api, 'tests', whitelist=r'.*test.py')
+  results = []
+
+  # affected_files is list of files affected by this change. The paths are
+  # relative to the directory containing PRESUBMIT.py.
+  affected_files = [
+      input_api.os_path.relpath(f, input_api.PresubmitLocalPath())
+      for f in input_api.AbsoluteLocalPaths()]
+
+  # Run the chromium.ycm_extra_conf_unittest test if the YCM config file is
+  # changed or if any change is affecting the tests directory. This specific
+  # test requires access to 'ninja' and hasn't been tested on platforms other
+  # than Linux.
+  if 'chromium.ycm_extra_conf.py' in affected_files or \
+      any([input_api.re.match(r'tests(/|\\)',f) for f in affected_files]):
+    results += input_api.RunTests(
+        input_api.canned_checks.GetUnitTests(
+            input_api, output_api,
+            ['tests/chromium.ycm_extra_conf_unittest.py']))
+
+  return results