BUG=
R=nweiz@google.com

Review URL: https://codereview.chromium.org//2557183002 .

Dartium wasn't emitting any standard IO on Windows, which caused us to
stall out waiting for the Observatory URL in debug mode.

See dart-lang/sdk#28034
Closes #425

Closes #503

Review URL: https://codereview.chromium.org//2526223002 .

Fixes #436.

R=nweiz@google.com

Review URL: https://codereview.chromium.org//2515303002 .

I think most of these breakages are due to the 1325b694 merge being
slightly busted.

Add debugging support for the JSON reporter.

Also update the pubspec and changelog.

External tools can use this to communicate with the test runner.

This tracks configuration that makes sense to apply to test suites, as
opposed to Configuration which applies to an entire run and Metadata
which applies to individual tests. This is intended to make it easier
for load separate configurations for separate targets in a live test
runner.

If a web test emitted any kind of message after the browser manager was
closed, the debugging timer would reset and cause the VM not to exit for
an extra three seconds.

Previously, the --precompiled flag only overlayed precompiled JS; all
HTML-file handling was left up to the test package. But the internal
Google infrastructure wants to be able to generate the HTML as well.
This changes the semantics so that both JS and HTML are expected in the
precompiled directory.

Closes #458

Make test iframes visible when debugging.

Closes #429

Closes #485

R=nweiz@google.com
BUG=

Review URL: https://codereview.chromium.org//2392743005 .

This reverts commit 4ca058ce.

Closes #477

This will be useful for Bolt, which has out-of-band information about
what platforms each given test is intended to run on.

Don't capture stack traces by default.

Stack traces are now only captured for the JSON reporter. Capturing
traces was slow enough to be a serious problem for test suites with many
tests.

Closes #457

This introduces a zone-scoped `Configuration.current`. This makes it
much easier to propagate the configuration everywhere it needs to go,
especially to plugins.

Now that https://codereview.chromium.org/1241723003/ has landed

R=keertip@google.com

Review URL: https://codereview.chromium.org//2379083002 .

It was printing the wrong number of seconds for durations longer than a
minute.

Closes #463

Closes #461

R=nweiz@google.com

Review URL: https://codereview.chromium.org//2285133005 .

There is still a warning before of 'expectAsync', but this would
require making it generic, which is outside of the scope of this CL.

R=brianwilkerson@google.com, rnystrom@google.com, nweiz@google.com
BUG=

Review URL: https://codereview.chromium.org//2282003002 .

The Dartium versions that didn't support this are long since out of
circulation.

R=jakemac@google.com

Review URL: https://codereview.chromium.org//2272223003 .