[Tests] Disable flaky NetworkErrorLoggingEndToEndTest.UploadAtShutdown

- This test was frequently timing out the net_unittests on multiple
platforms.

TBR=juliatuttle@chromium.org

Bug: 820950
Change-Id: I1e24c286824b678db290ad1116f463c314a045cd
Reviewed-on: https://chromium-review.googlesource.com/964661Reviewed-by: Anita Woodruff <awdf@chromium.org>
Commit-Queue: Anita Woodruff <awdf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543448}

net/network_error_logging/network_error_logging_end_to_end_test.cc

@@ -199,7 +199,8 @@ TEST_F(NetworkErrorLoggingEndToEndTest, ReportNetworkError) {
 
 // Make sure an upload that is in progress at shutdown does not crash.
 // This verifies that https://crbug.com/792978 is fixed.
-TEST_F(NetworkErrorLoggingEndToEndTest, UploadAtShutdown) {
+// Disabled due to frequent timeouts - see https://crbug.com/820950 .
+TEST_F(NetworkErrorLoggingEndToEndTest, DISABLED_UploadAtShutdown) {
   upload_should_hang_ = true;
 
   TestDelegate configure_delegate;