[ffi/samples] Avoid using mismatched strdup/CoTaskMemFree on Windows.

Fixes https://github.com/dart-lang/sdk/issues/61307
TEST=samples/ffi/http on windows

Change-Id: Ibc900896ccb0ea1472b4360cfb7b615fc06efd87
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/445108
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Liam Appelbe <liama@google.com>

samples/ffi/http/lib/fake_http.cc

@@ -34,7 +34,7 @@ Content-Type: text/html; charset=UTF-8
 DART_EXPORT void http_get(const char* uri, void (*onResponse)(const char*)) {
   std::thread([onResponse]() {
     std::this_thread::sleep_for(std::chrono::seconds(3));
-    onResponse(strdup(kExampleResponse));
+    onResponse(kExampleResponse);
   }).detach();
 }
 
@@ -42,7 +42,7 @@ DART_EXPORT void http_serve(void (*onRequest)(const char*)) {
   std::thread([onRequest]() {
     while (true) {
       std::this_thread::sleep_for(std::chrono::seconds(1));
-      onRequest(strdup(kExampleRequest));
+      onRequest(kExampleRequest);
     }
   }).detach();
 }

samples/ffi/http/lib/http.dart

@@ -17,7 +17,6 @@ Future<String> httpGet(String uri) async {
   final completer = Completer<String>();
   void onResponse(Pointer<Utf8> responsePointer) {
     completer.complete(responsePointer.toDartString());
-    calloc.free(responsePointer);
   }
 
   final callback = NativeCallable<HttpCallback>.listener(onResponse);
@@ -44,7 +43,6 @@ void httpServe(void Function(String) onRequest) {
   // Create the NativeCallable.listener.
   void onNativeRequest(Pointer<Utf8> requestPointer) {
     onRequest(requestPointer.toDartString());
-    calloc.free(requestPointer);
   }
 
   final callback = NativeCallable<HttpCallback>.listener(onNativeRequest);