remoting: increase security key timeout for tests

On the slower macOS bots, this test sometimes takes ~150ms longer
than kLargeResponseTimeoutMs for some of the timeout tests, so bump
up the threshold for success.

Bug: 905265
Change-Id: I0a968a0075d5ea7448f327a07ec36389de25fe7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1642737
Auto-Submit: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666263}

remoting/host/security_key/security_key_ipc_server_unittest.cc

@@ -27,7 +27,7 @@
 namespace {
 const int kTestConnectionId = 42;
 const int kInitialConnectTimeoutMs = 250;
-const int kConnectionTimeoutErrorDeltaMs = 100;
+const int kConnectionTimeoutErrorDeltaMs = 250;
 const int kLargeResponseTimeoutMs = 500;
 const int kLargeMessageSizeBytes = 256 * 1024;
 }  // namespace