[dart:io] Allow setting overrides in the root Zone

Otherwise there is no way to install overrides that affect the whole
program.

related https://github.com/flutter/flutter/issues/13602

Change-Id: I905b7067e79f11051e8204ebb296915d495fd13f
Reviewed-on: https://dart-review.googlesource.com/30100
Reviewed-by: Florian Loitsch <floitsch@google.com>
Commit-Queue: Zach Anderson <zra@google.com>

sdk/lib/_http/overrides.dart

@@ -30,8 +30,19 @@ const _asyncRunZoned = runZoned;
 /// }
 /// ```
 abstract class HttpOverrides {
+  static HttpOverrides _global;
+
   static HttpOverrides get current {
-    return Zone.current[_httpOverridesToken];
+    return Zone.current[_httpOverridesToken] ?? _global;
+  }
+
+  /// The [HttpOverrides] to use in the root [Zone].
+  ///
+  /// These are the [HttpOverrides] that will be used in the root Zone, and in
+  /// Zone's that do not set [HttpOverrides] and whose ancestors up to the root
+  /// Zone do not set [HttpOverrides].
+  static set global(HttpOverrides overrides) {
+    _global = overrides;
   }
 
   /// Runs [body] in a fresh [Zone] using the provided overrides.

sdk/lib/io/overrides.dart

@@ -32,8 +32,19 @@ const _asyncRunZoned = runZoned;
 /// }
 /// ```
 abstract class IOOverrides {
+  static IOOverrides _global;
+
   static IOOverrides get current {
-    return Zone.current[_ioOverridesToken];
+    return Zone.current[_ioOverridesToken] ?? _global;
+  }
+
+  /// The [IOOverrides] to use in the root [Zone].
+  ///
+  /// These are the [IOOverrides] that will be used in the root Zone, and in
+  /// Zone's that do not set [IOOverrides] and whose ancestors up to the root
+  /// Zone do not set [IOOverrides].
+  static set global(IOOverrides overrides) {
+    _global = overrides;
   }
 
   /// Runs [body] in a fresh [Zone] using the provided overrides.

tests/standalone/io/http_override_test.dart

@@ -171,9 +171,39 @@ zonedWithHttpOverridesTest() {
   }, new MyHttpOverrides());
 }
 
+globalHttpOverridesTest() {
+  HttpOverrides.global = new MyHttpOverrides();
+  var httpClient = new HttpClient();
+  Expect.isNotNull(httpClient);
+  Expect.isTrue(httpClient is MyHttpClient1);
+  Expect.equals((new MyHttpClient1(null)).userAgent, httpClient.userAgent);
+  HttpOverrides.global = null;
+  httpClient = new HttpClient();
+  Expect.isTrue(httpClient is HttpClient);
+  Expect.isTrue(httpClient is! MyHttpClient1);
+}
+
+globalHttpOverridesZoneTest() {
+  HttpOverrides.global = new MyHttpOverrides();
+  runZoned(() {
+    runZoned(() {
+      var httpClient = new HttpClient();
+      Expect.isNotNull(httpClient);
+      Expect.isTrue(httpClient is MyHttpClient1);
+      Expect.equals((new MyHttpClient1(null)).userAgent, httpClient.userAgent);
+    });
+  });
+  HttpOverrides.global = null;
+  var httpClient = new HttpClient();
+  Expect.isTrue(httpClient is HttpClient);
+  Expect.isTrue(httpClient is! MyHttpClient1);
+}
+
 main() {
   withHttpOverridesTest();
   nestedWithHttpOverridesTest();
   nestedDifferentOverridesTest();
   zonedWithHttpOverridesTest();
+  globalHttpOverridesTest();
+  globalHttpOverridesZoneTest();
 }

tests/standalone/io/io_override_test.dart

@@ -196,6 +196,34 @@ Future<Null> ioOverridesRunTest() async {
   await f;
 }
 
+class MyIOOverrides extends IOOverrides {
+  Directory createDirectory(String path) => DirectoryMock.createDirectory(path);
+}
+
+globalIOOverridesTest() {
+  IOOverrides.global = new MyIOOverrides();
+  Expect.isTrue(new Directory("directory") is DirectoryMock);
+  IOOverrides.global = null;
+  Directory dir = new Directory("directory");
+  Expect.isTrue(dir is! DirectoryMock);
+  Expect.isTrue(dir is Directory);
+}
+
+globalIOOverridesZoneTest() {
+  IOOverrides.global = new MyIOOverrides();
+  runZoned(() {
+    runZoned(() {
+      Expect.isTrue(new Directory("directory") is DirectoryMock);
+    });
+  });
+  IOOverrides.global = null;
+  Directory dir = new Directory("directory");
+  Expect.isTrue(dir is! DirectoryMock);
+  Expect.isTrue(dir is Directory);
+}
+
 main() async {
   await ioOverridesRunTest();
+  globalIOOverridesTest();
+  globalIOOverridesZoneTest();
 }