[fuchsia] Reduce the features enabled for isolated Contexts.

Isolated contexts are designed for "web UI" content, which should only
require basic audio and rendering features.

Bug: b/143575823
Change-Id: I83c3cea67de8c61b2a85f0f05729c1674c38ae76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1893525Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Emircan Uysaler <emircan@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711520}

fuchsia/runners/cast/cast_runner.cc

@@ -33,9 +33,13 @@ bool AreCastComponentParamsValid(
 fuchsia::web::CreateContextParams BuildCreateContextParamsForIsolatedRunners(
     const fuchsia::web::CreateContextParams& create_context_params) {
   fuchsia::web::CreateContextParams output;
-  if (create_context_params.has_features()) {
-    output.set_features(create_context_params.features());
-  }
+
+  // Isolated contexts receive only a limited set of features.
+  output.set_features(
+      fuchsia::web::ContextFeatureFlags::AUDIO |
+      fuchsia::web::ContextFeatureFlags::VULKAN |
+      fuchsia::web::ContextFeatureFlags::HARDWARE_VIDEO_DECODER);
+
   if (create_context_params.has_user_agent_product()) {
     output.set_user_agent_product(create_context_params.user_agent_product());
   }