[fuchsia] Reduce logging level for CastRunner.

Prevents excessive logspam from being emitted to the Fuchsia logging
service from third party JS logging code.

Improves application runtime performance and Archivist memory
footprint.

Bug: b/157682779
Change-Id: I5304c52962d980d60be612696bcab8846cb52677
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2220360
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Auto-Submit: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772931}

fuchsia/runners/cast/cast_component.cc

@@ -92,6 +92,7 @@ void CastComponent::StartComponent() {
                                fuchsia::web::AllowInputState::DENY);
   frame()->SetNavigationEventListener(
       navigation_listener_binding_.NewBinding());
+  frame()->SetJavaScriptLogLevel(fuchsia::web::ConsoleLogLevel::WARN);
 
   if (IsAppConfigForCastStreaming(application_config_)) {
     // TODO(crbug.com/1082821): Remove this once the Cast Streaming Receiver