Test for shill::kErrorNoFailure in NetworkState

TBR=khormimoto@chromium.org

Bug: 931070
Change-Id: I820336ff5b53baff9c9dddf6dbb7373f9020339e
Reviewed-on: https://chromium-review.googlesource.com/c/1470746
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Auto-Submit: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632048}

chromeos/network/network_state.cc

@@ -540,8 +540,10 @@ bool NetworkState::NetworkStateIsCaptivePortal(
 
 // static
 bool NetworkState::ErrorIsValid(const std::string& error) {
-  // Shill uses "Unknown" to indicate an unset or cleared error state.
-  return !error.empty() && error != kErrorUnknown;
+  // Pre M-74 Shill uses "Unknown" to indicate an unset or cleared error state.
+  // TODO(stevenjb): Remove kErrorUnknown once 74 has shipped.
+  return !error.empty() && error != kErrorUnknown &&
+         error != shill::kErrorNoFailure;
 }
 
 // static