Add support for ArrayBufferView as POST body

Section 6.2 of the spec says that body can be BufferSource.
BufferSource is defined in https://heycam.github.io/webidl/#BufferSource:

> The BufferSource typedef is used to represent objects that are either
> themselves an ArrayBuffer or which provide a view on to an ArrayBuffer.

Furthermore, passing an ArrayBuffer directly to XMLHttpRequest is
considered deprecated and Safari throws a warning about it. This makes
it even more important to support ArrayBufferView in fetch.

The fallback for `ArrayBuffer.isView` is provided for IE 10, which
doesn't implement the method.

fetch.js

@@ -20,6 +20,24 @@
     arrayBuffer: 'ArrayBuffer' in self
   }
 
+  if (support.arrayBuffer) {
+    var viewClasses = [
+      '[object Int8Array]',
+      '[object Uint8Array]',
+      '[object Uint8ClampedArray]',
+      '[object Int16Array]',
+      '[object Uint16Array]',
+      '[object Int32Array]',
+      '[object Uint32Array]',
+      '[object Float32Array]',
+      '[object Float64Array]'
+    ]
+
+    var isArrayBufferView = ArrayBuffer.isView || function(obj) {
+      return obj && viewClasses.indexOf(Object.prototype.toString.call(obj)) > -1
+    }
+  }
+
   function normalizeName(name) {
     if (typeof name !== 'string') {
       name = String(name)
@@ -177,7 +195,7 @@
         this._bodyText = body.toString()
       } else if (!body) {
         this._bodyText = ''
-      } else if (support.arrayBuffer && ArrayBuffer.prototype.isPrototypeOf(body)) {
+      } else if (support.arrayBuffer && (ArrayBuffer.prototype.isPrototypeOf(body) || isArrayBufferView(body))) {
         // Only support ArrayBuffers for POST method.
         // Receiving ArrayBuffers happens via Blobs, instead.
       } else {

test/test.js

@@ -868,15 +868,29 @@ suite('fetch method', function() {
       })
     })
 
-    featureDependent(test, support.arrayBuffer, 'sends ArrayBuffer body', function() {
-      return fetch('/request', {
-        method: 'post',
-        body: arrayBufferFromText('name=Hubot')
-      }).then(function(response) {
-        return response.json()
-      }).then(function(request) {
-        assert.equal(request.method, 'POST')
-        assert.equal(request.data, 'name=Hubot')
+    featureDependent(suite, support.arrayBuffer, 'ArrayBuffer', function() {
+      test('ArrayBuffer body', function() {
+        return fetch('/request', {
+          method: 'post',
+          body: arrayBufferFromText('name=Hubot')
+        }).then(function(response) {
+          return response.json()
+        }).then(function(request) {
+          assert.equal(request.method, 'POST')
+          assert.equal(request.data, 'name=Hubot')
+        })
+      })
+
+      test('TypedArray body', function() {
+        return fetch('/request', {
+          method: 'post',
+          body: new Uint8Array(arrayBufferFromText('name=Hubot'))
+        }).then(function(response) {
+          return response.json()
+        }).then(function(request) {
+          assert.equal(request.method, 'POST')
+          assert.equal(request.data, 'name=Hubot')
+        })
       })
     })