Add --canary flag to gradle project test and update gradle.

This flag enables support for Android Studio 3.0 which allows us to use
Java 8 features. Gradle is updated to version 4.1.0.

BUG=webrtc:8084

Review-Url: https://codereview.webrtc.org/2994123002
Cr-Commit-Position: refs/heads/master@{#19319}

DEPS

@@ -114,7 +114,7 @@ deps_os = {
     # Gradle 3.5.0. Used for testing Android Studio project generation for WebRTC.
     'src/webrtc/examples/androidtests/third_party/gradle':
       Var('chromium_git') + '/external/github.com/gradle/gradle.git' + '@' +
-      'b762622a185d59ce0cfc9cbc6ab5dd22469e18a6',
+      '941559e020f6c357ebb08d5c67acdb858a3defc2',
   },
   'ios': {
     'src/ios':

webrtc/examples/androidtests/gradle_project_test.py

@@ -64,7 +64,7 @@ def main():
     _RunCommand([GENERATE_GRADLE_SCRIPT, '--output-directory', output_dir,
         '--target', '//webrtc/examples:AppRTCMobile',
         '--project-dir', project_dir,
-        '--use-gradle-process-resources', '--split-projects'])
+        '--use-gradle-process-resources', '--split-projects', '--canary'])
     _RunCommand([GRADLEW_BIN, 'assembleDebug'], project_dir)
   finally:
     # Do not delete temporary directory if user specified it manually.