Actually disable Fast Refresh

Author: bvaughn

packages/react-refresh/src/ReactFreshRuntime.js

@@ -464,13 +464,18 @@ export function injectIntoGlobalHook(globalObject: any): void {
         onCommitFiberUnmount() {},
       };
     }
-    // Checks if DevTools hook is disabled
+
     if (hook.isDisabled) {
+      // This isn't a real property on the hook, but it can be set to opt out
+      // of DevTools integration and associated warnings and logs.
+      // Using console['warn'] to evade Babel and ESLint
       console['warn'](
         'Something has shimmed the React DevTools global hook (REACT_DEVTOOLS_GLOBAL_HOOK). ' +
           'Fast Refresh is not compatible with this shim and will be disabled.',
       );
+      return;
     }
+
     // Here, we just want to get a reference to scheduleRefresh.
     const oldInject = hook.inject;
     hook.inject = function(injected) {