[dart:html] Add SharedArrayBuffer constructor and slice

Fixes https://github.com/dart-lang/sdk/issues/35344

Change-Id: I5742adddf1fe01bfe40860a734a4c930091d8472
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/253563
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Kevin Moore <kevmoo@google.com>

CHANGELOG.md

@@ -55,11 +55,17 @@ Updated the Linter to `1.26.0`, which includes changes that
   non-final variable.
 - fix`use_build_context_synchronously` to handle `await`s in `if` conditions.
 
+### Core libraries
+
 #### `dart:io`
 
 - **Breaking Change** [#49305](https://github.com/dart-lang/sdk/issues/49305):
   Disallow negative or hexadecimal content-length headers.
 
+#### `dart:html`
+
+- Add constructor and `slice` to `SharedArrayBuffer`.
+
 ## 2.18.0
 
 ### Language

sdk/lib/html/dart2js/html_dart2js.dart

@@ -28225,7 +28225,20 @@ class SharedArrayBuffer extends JavaScriptObject {
     throw new UnsupportedError("Not supported");
   }
 
+  factory SharedArrayBuffer([int? length]) {
+    if (length != null) {
+      return SharedArrayBuffer._create_1(length);
+    }
+    return SharedArrayBuffer._create_2();
+  }
+  static SharedArrayBuffer _create_1(length) =>
+      JS('SharedArrayBuffer', 'new SharedArrayBuffer(#)', length);
+  static SharedArrayBuffer _create_2() =>
+      JS('SharedArrayBuffer', 'new SharedArrayBuffer()');
+
   int? get byteLength native;
+
+  SharedArrayBuffer slice([int? begin, int? end]) native;
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a

tools/dom/dom.json

@@ -21240,8 +21240,12 @@
   },
   "SharedArrayBuffer": {
     "members": {
+      "SharedArrayBuffer": {},
       "byteLength": {
         "support_level": "untriaged"
+      },
+      "slice": {
+        "support_level": "untriaged"
       }
     },
     "support_level": "untriaged"

tools/dom/idl/dart/dart.idl

@@ -683,3 +683,10 @@ interface NoncedElement {
 callback PositionCallback = void(object position);
 
 interface MathMLElement : Element {};
+
+[DartSupplemental,
+  CustomConstructor,
+  Constructor(optional unsigned long length)
+] interface SharedArrayBuffer {
+    SharedArrayBuffer slice(optional unsigned long begin, optional unsigned long end);
+};