Update PushEvent and PushMessageData to match the spec.

LayoutTests/http/tests/push_messaging/resources/pushmessagedata-constructor-text.js

-importScripts('../../serviceworker/resources/worker-testharness.js');
-importScripts('/resources/testharness-helpers.js');
-
-test(function() {
-    var data = new PushMessageData('Hello, world!');
-    assert_equals(data.text(), 'Hello, world!');
-
-}, 'PushMessageData can be constructed with a string parameter.');
-
-test(function() {
-    var event = new PushEvent('PushEvent');
-
-    assert_equals(event.data.arrayBuffer().byteLength, 0);
-
-    assert_equals(event.data.blob().size, 0);
-    assert_equals(event.data.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 {
-      event.data.json();
-    } catch (eventDataException) {
-      try {
-        JSON.parse('');
-      } catch (jsonParseException) {
-        assert_equals(eventDataException.name, jsonParseException.name);
-        assert_equals(eventDataException.message, jsonParseException.message);
-      }
-    }
-
-    assert_equals(event.data.text().length, 0);
-
-}, 'PushMessageData is empty by default, given a PushEvent constructor.');
-
-test(function() {
-    var event = new PushEvent('PushEvent', {
-        data: new PushMessageData('FOOBAR')
-    });
-
-    var arrayBuffer = event.data.arrayBuffer();
-    assert_equals(arrayBuffer.byteLength, 6);
-
-    var int8Array = new Int8Array(arrayBuffer);
-    assert_equals(int8Array[0], 70); // F
-    assert_equals(int8Array[3], 66); // B
-
-}, 'Reading an ArrayBuffer from PushMessageData through the PushEvent constructor.');
-
-async_test(function(test) {
-    var event = new PushEvent('PushEvent', {
-        data: new PushMessageData('FOOBAR')
-    });
-
-    var blob = event.data.blob();
-    assert_equals(blob.size, 6);
-    assert_equals(blob.type, '');
-
-    var reader = new FileReader();
-    reader.addEventListener('load', function() {
-      assert_equals(reader.result, 'FOOBAR');
-      test.done();
-    });
-
-    reader.readAsText(blob);
-
-}, 'Reading a Blob from PushMessageData through the PushEvent constructor.')
-
-test(function() {
-    var event = new PushEvent('PushEvent', {
-        data: new PushMessageData('[5, 6, 7]')
-    });
-
-    var array = event.data.json();
-    assert_equals(array.length, 3);
-    assert_equals(array[1], 6);
-
-    event = new PushEvent('PushEvent', {
-        data: new PushMessageData('{ "foo": { "bar": 42 } }')
-    });
-
-    assert_equals(event.data.json().foo.bar, 42);
-
-}, 'Reading JSON from PushMessageData through the PushEvent constructor.');
-
-test(function() {
-    var event = new PushEvent('PushEvent', {
-        data: new PushMessageData('Hello, world!')
-    });
-
-    assert_equals(event.data.text(), 'Hello, world!');
-
-}, 'Reading text from PushMessageData through the PushEvent constructor.');