Update PushEvent and PushMessageData to match the spec.

LayoutTests/http/tests/push_messaging/resources/pushmessagedata-worker.js

+importScripts('../../serviceworker/resources/worker-testharness.js');
+importScripts('/resources/testharness-helpers.js');
+
+function createPushMessageData(data)
+{
+    // The PushMessageData object does not expose a constructor, but we can get an object
+    // initialized with our data by constructing a PushEvent.
+    return new PushEvent('PushEvent', { data: data }).data;
+}
+
+test(function() {
+    const textContents = 'Hello, world!';
+
+    var runTest = pushEvent => {
+        assert_not_equals(pushEvent.data, null);
+        assert_equals(pushEvent.data.text(), textContents);
+    };
+
+    // JavaScript strings are UTF-16, whereas binary data for push message data will be
+    // encoded as UTF-8. Convert accordingly.
+    var bufferView = new TextEncoder('utf-8').encode(textContents);
+
+    runTest(new PushEvent('PushEvent', { data: bufferView }));
+    runTest(new PushEvent('PushEvent', { data: bufferView.buffer }));
+    runTest(new PushEvent('PushEvent', { data: textContents }));
+
+}, 'PushEvent can be initialized from ArrayBuffer, ArrayBufferView and USVStrings.');
+
+test(function() {
+    var pushMessageData = createPushMessageData();
+
+    assert_equals(pushMessageData.arrayBuffer().byteLength, 0);
+
+    assert_equals(pushMessageData.blob().size, 0);
+    assert_equals(pushMessageData.blob().type, '');
+
+    // PushMessageData.json() is specified to be identical to JSON.parse() with
+    // the message's data as the argument. JSON.parse('') throws an exception,
+    // so verify that calling json() without a body throws the same exception.
+    try {
+        pushMessageData.json();
+        assert_unreached('Expected an exception to be thrown.');
+    } catch (eventDataException) {
+        try {
+            JSON.parse('');
+            assert_unreached('Expected an exception to be thrown.');
+        } catch (jsonParseException) {
+            assert_equals(eventDataException.name, jsonParseException.name);
+            assert_equals(eventDataException.message, jsonParseException.message);
+        }
+    }
+
+    assert_equals(pushMessageData.text().length, 0);
+
+}, 'PushMessageData is empty by default.');
+
+test(function() {
+    const binaryContents = [1, 2, 3];
+    const textContents = 'FOOBAR';
+
+    var pushMessageDataBinary = createPushMessageData(new Uint8Array(binaryContents)),
+        pushMessageDataString = createPushMessageData(textContents);
+
+    var binaryBuffer = pushMessageDataBinary.arrayBuffer(),
+        binaryBufferView = new Uint8Array(binaryBuffer);
+
+    assert_equals(binaryBuffer.byteLength, binaryContents.length);
+    assert_array_equals(binaryBufferView, binaryContents);
+
+    var stringBuffer = pushMessageDataString.arrayBuffer(),
+        stringBufferView = new Int8Array(stringBuffer);
+
+    assert_equals(stringBufferView.length, textContents.length);
+    assert_equals(stringBufferView[0], 70 /* F */);
+    assert_equals(stringBufferView[3], 66 /* B */);
+
+}, 'PushMessageData handling of ArrayBuffer content.');
+
+async_test(function(test) {
+    const textContents = 'Hello, world!';
+
+    var pushMessageData = createPushMessageData(textContents);
+
+    var blob = pushMessageData.blob(),
+        reader = new FileReader();
+
+    assert_equals(blob.size, textContents.length);
+    assert_equals(blob.type, '');
+
+    reader.addEventListener('load', () => {
+        assert_equals(reader.result, textContents);
+        test.done();
+    });
+
+    reader.readAsText(blob);
+
+}, 'PushMessageData handling of Blob content.')
+
+test(function() {
+    var pushMessageDataArray = createPushMessageData('[5, 6, 7]'),
+        pushMessageDataObject = createPushMessageData('{ "foo": { "bar": 42 } }'),
+        pushMessageDataString = createPushMessageData('"foobar"');
+
+    var array = pushMessageDataArray.json();
+    assert_equals(array.length, 3);
+    assert_equals(array[1], 6);
+
+    var object = pushMessageDataObject.json();
+    assert_equals(object.foo.bar, 42);
+
+    var string = pushMessageDataString.json();
+    assert_equals(string, 'foobar');
+
+}, 'PushMessageData handling of valid JSON content.');
+
+test(function() {
+    // Note that we do not care about the exception code - it's pass through.
+    assert_throws(null, () => createPushMessageData('\\o/').json());
+
+}, 'PushMessageData handling of invalid JSON content.');
+
+test(function() {
+    assert_throws(null, () => new PushMessageData());
+    assert_throws(null, () => new PushMessageData('Hello, world!'));
+    assert_throws(null, () => new PushMessageData(new ArrayBuffer(8)));
+
+}, 'PushMessageData should not be constructable.');