Fix build warning in device_command_screenshot_job.cc

device_command_screenshot_job.cc:132:70: warning: 'result_code' may be used uninitialized in this function [-Wmaybe-uninitialized]

Review URL: https://codereview.chromium.org/1159163006

Cr-Commit-Position: refs/heads/master@{#333691}

chrome/browser/chromeos/policy/remote_commands/device_command_screenshot_job.cc

@@ -113,7 +113,7 @@ void DeviceCommandScreenshotJob::OnSuccess() {
 }
 
 void DeviceCommandScreenshotJob::OnFailure(UploadJob::ErrorCode error_code) {
-  ResultCode result_code;
+  ResultCode result_code = FAILURE_CLIENT;
   switch (error_code) {
     case UploadJob::AUTHENTICATION_ERROR:
       result_code = FAILURE_AUTHENTICATION;