Implement typed array constructors.

client/dom/generated/src/frog/Float32Array.dart

 
-class Float32Array extends ArrayBufferView native "*Float32Array" {
+class Float32Array extends ArrayBufferView implements List<num> native "Float32Array" {
+
+  factory Float32Array(int length) =>  _construct(length);
+
+  factory Float32Array.fromList(List<num> list) => _construct(list);
+
+  factory Float32Array.fromBuffer(ArrayBuffer buffer) => _construct(buffer);
+
+  static _construct(arg) native 'return new Float32Array(arg);';
 
   static final int BYTES_PER_ELEMENT = 4;
 
   int length;
 
+  num operator[](int index) native;
+
+  void operator[]=(int index, num value) native;
+
   Float32Array subarray(int start, [int end = null]) native;
 }