Revert "[dart:html] Move NullWindowException to implementation"

This reverts commit 14a3051552.

Reason for revert: b/289195983

Original change's description:
> [dart:html] Move NullWindowException to implementation
>
> Window.open may open a null window in more cases than expected.
> Users may not care that the window they get back is invalid if
> they never use it. Therefore, this CL moves the exception to
> the implementation of the returned window in order to reduce
> noise, but still give a way for users to recover if they wish
> to do so.
>
> CoreLibraryReviewExempt: Backend-specific library.
> Change-Id: I005cf80630cfb4db2f5ec2012cfcd0161ad10ff1
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/311460
> Commit-Queue: Srujan Gaddam <srujzs@google.com>
> Reviewed-by: Sigmund Cherem <sigmund@google.com>

Change-Id: Id7c514a80fdcaa18a7eb0acdcb7f36477a04d966
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/311843
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Auto-Submit: Ivan Inozemtsev <iinozemtsev@google.com>

CHANGELOG.md

@@ -36,6 +36,14 @@
 [#51486]: https://github.com/dart-lang/sdk/issues/51486
 [#52027]: https://github.com/dart-lang/sdk/issues/52027
 
+#### `dart:html`
+
+- **Breaking change to Window.open**:
+  `Window.open` will now throw an exception that can be caught
+  (`NullWindowException`) if the opened window is null. Previously, this null
+  window would be wrapped, and there would be surprising runtime errors when any
+  member is used on the wrapper.
+
 #### `dart:js_interop`
 
 - **Object literal constructors**:

sdk/lib/html/dart2js/html_dart2js.dart

@@ -32154,6 +32154,8 @@ class Window extends EventTarget
   /**
    * Opens a new window.
    *
+   * Throws a NullWindowException if the opened window is null.
+   *
    * ## Other resources
    *
    * * [Window.open](https://developer.mozilla.org/en-US/docs/Web/API/Window.open)
@@ -32162,6 +32164,7 @@ class Window extends EventTarget
   WindowBase open(String url, String name, [String? options]) {
     final win =
         options == null ? _open2(url, name) : _open3(url, name, options);
+    if (win == null) throw new NullWindowException();
     return _DOMWindowCrossFrame._createSafe(win);
   }
 
@@ -33779,7 +33782,7 @@ class Window extends EventTarget
 class NullWindowException implements Exception {
   @override
   String toString() {
-    return 'Attempting to use a null window opened in Window.open.';
+    return 'Attempted to call Window.open with a null window.';
   }
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
@@ -40121,12 +40124,7 @@ class _DOMWindowCrossFrame implements WindowBase {
   // Private window.  Note, this is a window in another frame, so it
   // cannot be typed as "Window" as its prototype is not patched
   // properly.  Its fields and methods can only be accessed via JavaScript.
-  final Object? __window;
-
-  Object get _window {
-    if (__window == null) throw new NullWindowException();
-    return __window!;
-  }
+  final Object _window;
 
   // Fields.
   HistoryBase get history =>
@@ -40163,7 +40161,7 @@ class _DOMWindowCrossFrame implements WindowBase {
   }
 
   // Implementation support.
-  _DOMWindowCrossFrame(this.__window);
+  _DOMWindowCrossFrame(this._window);
 
   static WindowBase _createSafe(w) {
     if (identical(w, window)) {

tests/lib/html/window_test.dart

@@ -12,15 +12,12 @@ main() {
     expect(window.scrollY, 0);
   });
   test('open', () {
-    final valid = window.open('', 'blank');
-    valid.closed;
-    // A blank page with no access to the original window (noopener) should
-    // result in null.
-    final invalid = window.open('', 'invalid', 'noopener=true');
+    window.open('', 'blank');
     try {
-      // Should result in an exception since the underlying window is null.
-      invalid.closed;
-      fail('Expected invalid.closed to throw.');
+      // A blank page with no access to the original window (noopener) should
+      // result in null.
+      window.open('', 'invalid', 'noopener=true');
+      fail('Expected Window.open to throw.');
     } on NullWindowException {}
   });
 }

tests/lib_2/html/window_test.dart

@@ -13,16 +13,4 @@ main() {
     expect(window.scrollX, 0);
     expect(window.scrollY, 0);
   });
-  test('open', () {
-    final valid = window.open('', 'blank');
-    valid.closed;
-    // A blank page with no access to the original window (noopener) should
-    // result in null.
-    final invalid = window.open('', 'invalid', 'noopener=true');
-    try {
-      // Should result in an exception since the underlying window is null.
-      invalid.closed;
-      fail('Expected invalid.closed to throw.');
-    } on NullWindowException {}
-  });
 }

tools/dom/src/dart2js_DOMImplementation.dart

@@ -9,12 +9,7 @@ class _DOMWindowCrossFrame implements WindowBase {
   // Private window.  Note, this is a window in another frame, so it
   // cannot be typed as "Window" as its prototype is not patched
   // properly.  Its fields and methods can only be accessed via JavaScript.
-  final Object? __window;
-
-  Object get _window {
-    if (__window == null) throw new NullWindowException();
-    return __window!;
-  }
+  final Object _window;
 
   // Fields.
   HistoryBase get history =>
@@ -51,7 +46,7 @@ class _DOMWindowCrossFrame implements WindowBase {
   }
 
   // Implementation support.
-  _DOMWindowCrossFrame(this.__window);
+  _DOMWindowCrossFrame(this._window);
 
   static WindowBase _createSafe(w) {
     if (identical(w, window)) {

tools/dom/templates/html/impl/impl_Window.darttemplate

@@ -50,6 +50,8 @@ $(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
   /**
    * Opens a new window.
    *
+   * Throws a NullWindowException if the opened window is null.
+   *
    * ## Other resources
    *
    * * [Window.open](https://developer.mozilla.org/en-US/docs/Web/API/Window.open)
@@ -58,6 +60,7 @@ $(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
   WindowBase open(String url, String name, [String$NULLABLE options]) {
     final win =
         options == null ? _open2(url, name) : _open3(url, name, options);
+    if (win == null) throw new NullWindowException();
     return _DOMWindowCrossFrame._createSafe(win);
   }
 
@@ -256,6 +259,6 @@ $!MEMBERS
 class NullWindowException implements Exception {
   @override
   String toString() {
-    return 'Attempting to use a null window opened in Window.open.';
+    return 'Attempted to call Window.open with a null window.';
   }
 }