Web component test framework (wcTest.BrowserTest)

Web component test framework (wcTest.BrowserTest)

This is the 3rd of 3 CLs to enable support for testing web
components in Chrome. This provides the wcTest.BrowserTest
framework for writing async Polymer tests using Mocha.

Based on first two patches:
1. http://crrev.com/1128543002
2. http://crrev.com/1124873002

A sample test is included (CrElementsBrowserTest), which
currently only references one set of tests (for cr-checkbox)
but is intended to cover all cr-elements in
ui/webui/resources/cr_elements.

Other tests which also extend wcTest.BrowserTest will be
developed, such as a test suite for Settings elements.

BUG=482770

[michaelpg, 2015-05-05 22:19:50]

Episode III: Revenge of the Sith.

https://codereview.chromium.org/1130553002/diff/1/chrome/test/data/webui/cr_c...
File chrome/test/data/webui/cr_checkbox_tests.js (right):

https://codereview.chromium.org/1130553002/diff/1/chrome/test/data/webui/cr_c...
chrome/test/data/webui/cr_checkbox_tests.js:1: // Copyright 2015 The Chromium
Authors. All rights reserved.
It may make more sense to locate these tests alongside the source files, e.g. in
ui/webui/resources/cr_elements/cr_checkbox in this case.

[Jeremy Klein, 2015-05-06 18:03:35]

jlklein@chromium.org changed reviewers:
+ jlklein@chromium.org

[Jeremy Klein, 2015-05-06 18:03:36]

Cool stuff :-)

https://codereview.chromium.org/1130553002/diff/1/chrome/test/data/webui/cr_c...
File chrome/test/data/webui/cr_checkbox_tests.js (right):

https://codereview.chromium.org/1130553002/diff/1/chrome/test/data/webui/cr_c...
chrome/test/data/webui/cr_checkbox_tests.js:1: // Copyright 2015 The Chromium
Authors. All rights reserved.
On 2015/05/05 22:19:50, michaelpg wrote:
> It may make more sense to locate these tests alongside the source files, e.g.
in
> ui/webui/resources/cr_elements/cr_checkbox in this case.

+1 to keeping tests by their unit under test if possible.

https://codereview.chromium.org/1130553002/diff/1/chrome/test/data/webui/cr_c...
chrome/test/data/webui/cr_checkbox_tests.js:20: checkbox =
document.createElement('cr-checkbox');
Think it would be simple to use test-fixture for more complex dom structure? It
would let us do stuff like this:

https://github.com/PolymerElements/paper-checkbox/blob/master/test/basic.html...

But we'd need to be able to run the html rather than just js. Not worth a huge
effort, but would be convenient.

https://codereview.chromium.org/1130553002/diff/1/chrome/test/data/webui/cr_c...
chrome/test/data/webui/cr_checkbox_tests.js:54: checkbox.$.checkbox.tap();
note: iron-test-helpers has some useful bits we'll be able to use with 0.8,
particularly MockInteractions:

https://github.com/PolymerElements/iron-test-helpers