Add stack chain support to pub.

Add stack chain support to pub.

Specifically, when run with "--trace" or "--verbose", pub will capture its stack
chains and report them along with errors. Otherwise it should behave identically
to before.

R=rnystrom@google.com
BUG=8842
Committed: https://code.google.com/p/dart/source/detail?r=31176

[Bob Nystrom, 2013-12-17 00:18:03]

If I'm adding some random piece of functionality in pub that uses asynchrony,
how do I know what Chain stuff I need to wrap it in?

https://codereview.chromium.org/113453005/diff/1/sdk/lib/_internal/pub/lib/sr...
File sdk/lib/_internal/pub/lib/src/utils.dart (right):

https://codereview.chromium.org/113453005/diff/1/sdk/lib/_internal/pub/lib/sr...
sdk/lib/_internal/pub/lib/src/utils.dart:142: Future captureErrors(Future
callback(), {bool captureStackChains: false}) {
How about "captureErrorsIn"?

[nweiz, 2013-12-17 00:23:04]

The rule of thumb is to wrap [Chain.track] around any Future created by a dart:
library. This is annoying, but (in theory) it's temporary.

https://codereview.chromium.org/113453005/diff/1/sdk/lib/_internal/pub/lib/sr...
File sdk/lib/_internal/pub/lib/src/utils.dart (right):

https://codereview.chromium.org/113453005/diff/1/sdk/lib/_internal/pub/lib/sr...
sdk/lib/_internal/pub/lib/src/utils.dart:142: Future captureErrors(Future
callback(), {bool captureStackChains: false}) {
On 2013/12/17 00:18:03, Bob Nystrom wrote:
> How about "captureErrorsIn"?

I think it's clear when reading the code that you're capturing errors in the
callback. I'll change it if you want, but I think it makes it read worse.

[Bob Nystrom, 2013-12-17 00:24:10]

lgtm

[nweiz, 2013-12-17 00:26:56]

Committed patchset #1 manually as r31176 (presubmit successful).