Fix bunch of web test failures on Android and Fuchsia

A follow-up of crrev.com/611454. We had other instances of
LAYOUT_TEST_PATH_PREFIX.

TBR=qyesrsley@chromium.org
Bug: 909012
No-Try: true

Change-Id: Iec4c017f9123857f50e56ae3e8f5c6ae457af949
Reviewed-on: https://chromium-review.googlesource.com/c/1352087Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611561}

third_party/blink/tools/blinkpy/web_tests/port/android.py

@@ -1046,7 +1046,7 @@ class ChromiumAndroidDriver(driver.Driver):
     def _command_from_driver_input(self, driver_input):
         command = super(ChromiumAndroidDriver, self)._command_from_driver_input(driver_input)
         if command.startswith('/'):
-            command = 'http://127.0.0.1:8000' + LAYOUT_TEST_PATH_PREFIX + \
+            command = 'http://127.0.0.1:8000' + WEB_TESTS_PATH_PREFIX + \
                 '/' + self._port.relative_test_filename(command)
         return command
 

third_party/blink/tools/blinkpy/web_tests/port/fuchsia.py

@@ -280,7 +280,7 @@ class ChromiumFuchsiaDriver(driver.Driver):
         if command.startswith('/'):
             relative_test_filename = \
                 os.path.relpath(command, self._port.layout_tests_dir())
-            command = 'http://127.0.0.1:8000' + LAYOUT_TEST_PATH_PREFIX + \
+            command = 'http://127.0.0.1:8000' + WEB_TESTS_PATH_PREFIX + \
                 '/' + relative_test_filename
         return command