Move the PushMessagingBrowserTest to use SWR.showNotification().

Move the PushMessagingBrowserTest to use SWR.showNotification().

This will allow us to start throwing a TypeError per the specification
when constructing a new Notification object in a Service Worker.

This is part of a two-sided patch:
  [1] This patch.
  [2] https://codereview.chromium.org/923443005

BUG=459038
Committed: https://crrev.com/a4b68d8fa83978cf78c84398e852366188665c55
Cr-Commit-Position: refs/heads/master@{#316496}

[Peter Beverloo, 2015-02-16 17:36:45]

peter@chromium.org changed reviewers:
+ mvanouwerkerk@chromium.org

[Peter Beverloo, 2015-02-16 17:36:46]

PTAL

[Michael van Ouwerkerk, 2015-02-16 18:15:06]

lgtm - please add a bug number

[Peter Beverloo, 2015-02-16 18:21:40]

On 2015/02/16 18:15:06, Michael van Ouwerkerk wrote:
> lgtm - please add a bug number

Done. Thanks!

[Peter Beverloo, 2015-02-16 18:21:44]

The CQ bit was checked by peter@chromium.org

[commit-bot: I haz the power, 2015-02-16 18:22:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/930963002/1

[commit-bot: I haz the power, 2015-02-16 18:32:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-16 18:33:48]

Patchset 1 (id:??) landed as
https://crrev.com/a4b68d8fa83978cf78c84398e852366188665c55
Cr-Commit-Position: refs/heads/master@{#316496}