Add constructors for Float32Array and friends.

client/html/src/Uint8ArrayWrappingImplementation.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// WARNING: Do not edit - generated code.
-
 class Uint8ArrayWrappingImplementation extends ArrayBufferViewWrappingImplementation implements Uint8Array {
   Uint8ArrayWrappingImplementation._wrap(ptr) : super._wrap(ptr) {}
 
+  factory Uint8ArrayWrappingImplementation(int length) =>
+    LevelDom.wrapUint8Array(new dom.Uint8Array(length));
+
+  factory Uint8ArrayWrappingImplementation.from(List<num> list) =>
+    // TODO(nweiz): when there's a cross-platform name for the native
+    // implementation of List, check if [list] is native and if not convert it
+    // to a native list before sending it to the JS constructor.
+    LevelDom.wrapUint8Array(new dom.Uint8Array.fromList(list));
+
+  factory Uint8ArrayWrappingImplementation.fromBuffer(ArrayBuffer buffer) =>
+    LevelDom.wrapUint8Array(new dom.Uint8Array.fromBuffer(LevelDom.unwrap(buffer)));
+
   int get length() { return _ptr.length; }
 
   Uint8Array subarray(int start, [int end]) {
     if (end === null) {
       return LevelDom.wrapUint8Array(_ptr.subarray(start));
     } else {
       return LevelDom.wrapUint8Array(_ptr.subarray(start, end));
     }
   }
 }