Update dart_roller_helper.py to explicitly pass `--local-engine-hos…

…t` to the `flutter` tool. (#751)

Partial work towards flutter/flutter#132245.

These changes are intended to have no semantic change in behavior.
Currently the host configuration is _guessed_ by an internal heuristic,
but we're switching it to have an explicit configuration instead. In
other words, this is future proofing.

_(Worth noting, I'm not actually sure if it's important to have a
correct host configuration in release mode)_

tools/dart/dart_roll_helper.py

@@ -163,8 +163,9 @@ def run_flutter_doctor():
   print_status('Running flutter doctor')
   engine_src_path = '--local-engine-src-path={}'.format(engine_home())
   result = run_process(FLUTTER_DOCTOR + ['--local-engine=host_debug_unopt',
-                                    engine_src_path],
-                                    cwd=package_flutter_path())
+                                         '--local-engine-host=host_debug_unopt',
+                                         engine_src_path],
+                                         cwd=package_flutter_path())
   if result != 0:
     print_error('flutter doctor failed. Aborting roll.')
     sys.exit(ERROR_FLUTTER_DOCTOR_FAILED)
@@ -174,6 +175,7 @@ def run_tests():
   print_status('Running tests in packages/flutter')
   engine_src_path = '--local-engine-src-path={}'.format(engine_home())
   result = run_process(FLUTTER_TEST + ['--local-engine=host_debug_unopt',
+                                       '--local-engine-host=host_debug_unopt',
                                        engine_src_path],
                                        cwd=package_flutter_path())
   if result != 0:
@@ -182,6 +184,7 @@ def run_tests():
 
   print_status('Running tests in examples/flutter_gallery')
   result = run_process(FLUTTER_TEST + ['--local-engine=host_debug_unopt',
+                                       '--local-engine-host=host_debug_unopt',
                                        engine_src_path,
                                        '--disable-service-auth-codes'],
                                        cwd=flutter_gallery_path());
@@ -195,10 +198,12 @@ def run_hot_reload_configurations():
   engine_src_path = '--local-engine-src-path={}'.format(engine_home())
   run_process(FLUTTER_RUN + ['--release',
                              '--local-engine=android_release',
+                             '--local-engine-host=host_release',
                              engine_src_path],
                              cwd=flutter_gallery_path())
   print_status('Running flutter gallery debug')
   run_process(FLUTTER_RUN + ['--local-engine=android_debug_unopt',
+                             '--local-engine-host=host_debug_unopt',
                              engine_src_path],
                              cwd=flutter_gallery_path())