Respect git's ignore rules pervasively in pub.

sdk/lib/_internal/pub/test/serve/does_not_serve_gitignored_assets_test.dart

Index: sdk/lib/_internal/pub/test/serve/does_not_serve_gitignored_assets_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/serves_file_with_space_test.dart b/sdk/lib/_internal/pub/test/serve/does_not_serve_gitignored_assets_test.dart
similarity index 62%
copy from sdk/lib/_internal/pub/test/serve/serves_file_with_space_test.dart
copy to sdk/lib/_internal/pub/test/serve/does_not_serve_gitignored_assets_test.dart
index eead8082839c9d4283c884473baf40648f6c38a7..598ecf79010e2021a4dc1ac988ebe29832533b5e 100644
--- a/sdk/lib/_internal/pub/test/serve/serves_file_with_space_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/does_not_serve_gitignored_assets_test.dart
@@ -10,20 +10,23 @@ import 'utils.dart';
 
 main() {
   initConfig();
-  integration("serves a filename with a space", () {
-    d.dir(appPath, [
+  integration("doesn't serve .gitignored assets", () {
+    ensureGit();
+
+    d.git(appPath, [
       d.appPubspec(),
       d.dir("web", [
-        d.file("foo bar.txt", "outer contents"),
-        d.dir("sub dir", [
+        d.file("outer.txt", "outer contents"),
+        d.dir("dir", [
           d.file("inner.txt", "inner contents"),
         ])
-      ])
+      ]),
+      d.file(".gitignore", "/web/outer.txt\n/web/dir")
     ]).create();
 
     pubServe();
-    requestShouldSucceed("foo%20bar.txt", "outer contents");
-    requestShouldSucceed("sub%20dir/inner.txt", "inner contents");
+    requestShould404("outer.txt");
+    requestShould404("dir/inner.txt");
     endPubServe();
   });
 }