Android gtest runner: Only query device for test list when necessary

build/android/pylib/local/device/local_device_gtest_run.py

Index: build/android/pylib/local/device/local_device_gtest_run.py
diff --git a/build/android/pylib/local/device/local_device_gtest_run.py b/build/android/pylib/local/device/local_device_gtest_run.py
index 0f360d4a9e943045c946f68689f98788fd2966e9..c0903885d1f21098fcaceeb615e275be59c43b28 100644
--- a/build/android/pylib/local/device/local_device_gtest_run.py
+++ b/build/android/pylib/local/device/local_device_gtest_run.py
@@ -52,6 +52,32 @@ def PullAppFilesImpl(device, package, files, directory):
         break
     device.PullFile(device_file, host_file)
 
+
+def _ExtractTestsFromFilter(gtest_filter):
+  """Returns the list of tests specified by the given filter.
+
+  Returns:
+    None if the device should be queried for the test list instead.
+  """
+  # Empty means all tests, - means exclude filter.
+  if not gtest_filter or '-' in gtest_filter:
+    return None
+
+  patterns = gtest_filter.split(':')
+  # For a single pattern, allow it even if it has a wildcard so long as the
+  # wildcard comes at the end and there is at least one . to prove the scope is
+  # not too large.
+  # This heuristic is not necessarily faster, but normally is.
+  if len(patterns) == 1 and patterns[0].endswith('*'):
+    no_suffix = patterns[0].rstrip('*')
+    if '*' not in no_suffix and '.' in no_suffix:
+      return patterns
+
+  if '*' in gtest_filter:
+    return None
+  return patterns
+
+
 class _ApkDelegate(object):
   def __init__(self, test_instance):
     self._activity = test_instance.activity
@@ -229,8 +255,18 @@ class LocalDeviceGtestRun(local_device_test_run.LocalDeviceTestRun):
       tests = self._test_instance.FilterTests(tests)
       return tests
 
-    test_lists = self._env.parallel_devices.pMap(list_tests).pGet(None)
-    tests = list(sorted(set().union(*[set(tl) for tl in test_lists if tl])))
+    # When the list of tests to run is given via command-line, skip querying the

[jbudorick, 2015/10/13 17:17:48]

As written, this is structured in a way that implies that this extraction isn't
a very specialized case, which is a bit backwards.

As for an actionable nit: this can go before list_tests, since that isn't used
if we are able to extract a list of tests from the filter.

[agrieve, 2015/10/13 20:13:27]

Done (and updated comments to be a bit more special-casey.

+    # device (which takes ~3 seconds).
+    gtest_filter = self._test_instance.gtest_filter
+    tests = _ExtractTestsFromFilter(gtest_filter)
+
+    # Even when there's only one device, it still makes sense to retrieve the
+    # test list so that tests can be split up and run in batches rather than all
+    # at once (since test output is not streamed).
+    if not tests:
+      # Query all devices in case one fails.
+      test_lists = self._env.parallel_devices.pMap(list_tests).pGet(None)
+      tests = list(sorted(set().union(*[set(tl) for tl in test_lists if tl])))
     return tests
 
   #override