Android test_runner.py: Eliminate unused "adb devices" call for gtests

build/android/test_runner.py

Index: build/android/test_runner.py
diff --git a/build/android/test_runner.py b/build/android/test_runner.py
index 499ccb02c96674ea8ab80932130b67ed52bf77cd..8e468e32c465e07ebc93108c4dc3c89e4c32b599 100755
--- a/build/android/test_runner.py
+++ b/build/android/test_runner.py
@@ -916,29 +916,29 @@ def RunTestsCommand(args, parser): # pylint: disable=too-many-return-statements
   if args.enable_platform_mode:

[jbudorick, 2015/10/09 00:28:48]

alternatively, we could just switch this to

  if args.enable_platform_mode or command == 'gtest':

(this is where I'm going with https://codereview.chromium.org/1387933005/, but
that CL will take a little while)

[agrieve, 2015/10/09 00:58:54]

Interesting! Sounds good except with the change as-is it also skips the device
check for 'python' and 'junit'. Update description to mention this.

     return RunTestsInPlatformMode(args, parser)
 
-  if command in constants.LOCAL_MACHINE_TESTS:
-    devices = []
-  else:
-    devices = _GetAttachedDevices(args.blacklist_file, args.test_device)
-
   forwarder.Forwarder.RemoveHostLog()
   if not ports.ResetTestServerPortAllocation():
     raise Exception('Failed to reset test server port.')
 
+  def get_devices():
+    if command in constants.LOCAL_MACHINE_TESTS:
+      return []
+    return _GetAttachedDevices(args.blacklist_file, args.test_device)
+
   if command == 'gtest':
     return RunTestsInPlatformMode(args, parser)
   elif command == 'linker':
-    return _RunLinkerTests(args, devices)
+    return _RunLinkerTests(args, get_devices())
   elif command == 'instrumentation':
-    return _RunInstrumentationTests(args, devices)
+    return _RunInstrumentationTests(args, get_devices())
   elif command == 'uiautomator':
-    return _RunUIAutomatorTests(args, devices)
+    return _RunUIAutomatorTests(args, get_devices())
   elif command == 'junit':
     return _RunJUnitTests(args)
   elif command == 'monkey':
-    return _RunMonkeyTests(args, devices)
+    return _RunMonkeyTests(args, get_devices())
   elif command == 'perf':
-    return _RunPerfTests(args, devices)
+    return _RunPerfTests(args, get_devices())
   elif command == 'python':
     return _RunPythonTests(args)
   else: