Make failing HTTP requests thrown when using dart:io.

test/loader_http_test.dart

Index: test/loader_http_test.dart
diff --git a/test/loader_http_test.dart b/test/loader_http_test.dart
index 114ec6ac6bff01b8af1fa8527f8beff373772d83..7795f58c8c6d7f2ca70d158198ae1e1565931e3e 100644
--- a/test/loader_http_test.dart
+++ b/test/loader_http_test.dart
@@ -20,6 +20,12 @@ main() {
     int port = server.port;
     uri = Uri.parse("http://localhost:$port/default.html");
     server.forEach((HttpRequest request) {
+      if (request.uri.path.endsWith(".not")) {
+        request.response
+          ..statusCode = HttpStatus.NOT_FOUND
+          ..close();
+        return;
+      }
       var encodings = request.headers[HttpHeaders.ACCEPT_CHARSET];
       var encoding = parseAcceptCharset(encodings);
       request.response.headers.contentType =
@@ -61,6 +67,24 @@ main() {
     expect(buffer, content.codeUnits);
   });
 
+  test("not found - String", () async {
+    var loader = ResourceLoader.defaultLoader;
+    var badUri = uri.resolve("file.not");  // .not makes server fail.
+    expect(loader.readAsString(badUri), throws);
+  });
+
+  test("not found - bytes", () async {
+    var loader = ResourceLoader.defaultLoader;
+    var badUri = uri.resolve("file.not");  // .not makes server fail.
+    expect(loader.readAsBytes(badUri), throws);
+  });
+
+  test("not found - byte stream", () async {
+    var loader = ResourceLoader.defaultLoader;
+    var badUri = uri.resolve("file.not");  // .not makes server fail.
+    expect(loader.openRead(badUri).length, throws);
+  });
+
   tearDown(() {
     server.close();
     server = null;