This commit replaces our own infrastructure for handling browsers during
tests with Puppeteer. Using our own infrastructure for this had a few
downsides:
- It has proven to not always be reliable, especially when closing the
browser, causing failures on the bots because browsers were still
running even though they should have been stopped. Puppeteer should do
a better job with this because it uses the browser's test built-in
instrumentation tools for this (the devtools protocol) which our code
didn't. This also means that we don't have to pass
parameters/preferences to tweak browser behavior anymore.
- It requires the browsers under test to be installed on the system,
whereas Puppeteer downloads the browsers before the test. This means
that setup is much easier (no more manual installations and browser
manifest files) as well as testing with different browser versions
(since they can be provisioned on demand). Moreover, this ensures that
contributors always run the tests in both Firefox and Chrome,
regardless of which browsers they have installed locally.
- It's all code we have to maintain, so Puppeteer abstracts away how the
browsers start/stop for us so we don't have to keep that code.
By default, Puppeteer only installs one browser during installation,
hence the need for a post-install script to install the second browser.
This requires `cross-env` to make passing the environment variable work
on both Linux and Windows.
When reftest analyzer shows magnified pixels, there is a seemingly random offset between the mouse position and the magnified position. The reason for this is that reftest analyzer assumes all images have 800 * 1000 pixels but actually the test images have varying sizes.
The test runner is automated, so if the default browser test is
performed, the browser hangs waiting for user input it never gets.
Disable the test to fix that.
Moreover, enable E10s now that it is mature. This may help with the
performance of the test runner as well.
It's currently possible to step through the test results using the <kbd>N</kbd> and <kbd>P</kbd> keys, and you can also switch between test and reference images with the <kbd>T</kbd> key.
However if you want to highlight the differences, that can only be done by clicking. This has always annoyed me somewhat, so this patch adds support for toggling the differences view with the <kbd>D</kbd> key.
