[fuchsia] Report error status if reading existing interfaces fails.

NetworkChangeNotifier was mis-reporting the failure status as
ZX_ERR_INVALID_ARGS.  Move the failure logging into the
GetExistingInterfaces() call so that the status can be logged properly.

Bug: 1165716
Bug: b/177088778
Change-Id: I2e0db22ee27b93d1c5b3d199c6286d9898c2adf0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2623012
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843073}

net/base/network_change_notifier_fuchsia.cc

@@ -39,10 +39,9 @@ NetworkChangeNotifierFuchsia::NetworkChangeNotifierFuchsia(
   fuchsia::net::interfaces::WatcherSyncPtr watcher = handle.BindSync();
   base::Optional<internal::ExistingInterfaceProperties> interfaces =
       internal::GetExistingInterfaces(watcher);
-  if (!interfaces) {
-    ZX_LOG(ERROR, ZX_ERR_INVALID_ARGS) << "Failed to load existing interfaces";
+  if (!interfaces)
     return;
-  }
+
   handle = watcher.Unbind();
   bool notify_ip_address_changed = false;
   for (const auto& interface_entry : *interfaces) {

net/base/network_interfaces_fuchsia.cc

@@ -175,14 +175,17 @@ base::Optional<ExistingInterfaceProperties> GetExistingInterfaces(
   for (;;) {
     fuchsia::net::interfaces::Event event;
     zx_status_t status = watcher->Watch(&event);
-    if (status != ZX_OK)
+    if (status != ZX_OK) {
+      ZX_LOG(ERROR, status) << "GetExistingInterfaces: Watch() failed";
       return base::nullopt;
+    }
 
     switch (event.Which()) {
       case fuchsia::net::interfaces::Event::Tag::kExisting: {
         base::Optional<InterfaceProperties> interface =
             InterfaceProperties::VerifyAndCreate(std::move(event.existing()));
         if (!interface) {
+          LOG(ERROR) << "GetExistingInterfaces: Invalid kExisting event.";
           return base::nullopt;
         }
         uint64_t id = interface->id();
@@ -194,6 +197,7 @@ base::Optional<ExistingInterfaceProperties> GetExistingInterfaces(
         // fetching events.
         return existing_interfaces;
       default:
+        LOG(ERROR) << "GetExistingInterfaces: Unexpected event received.";
         return base::nullopt;
     }
   }