Add a cancel function which can cancel a context due to an error

[fanfuxiaoran]

Sometimes, we run mutilple go routines in a context, if one go routine
failed due to an error, we want to cancel the context and record the
error in it. So I added a function called WithErrorCancel function which
returns both CancelFunc and ErrorCancelFunc. CancelFunc is the same as
the function which is returned by WithCancel, ErrorCancelFunc is used to
cancel a context with an error.

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

---

What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
• The email used to register you as an authorized contributor must be the email used for the Git commit. Check your existing CLA data and verify that your email is set on your git commits.
• The email used to register you as an authorized contributor must also be attached to your GitHub account.

ℹ️ Googlers: Go here for more info.

[fanfuxiaoran]

@googlebot I signed it!

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.

[gopherbot]

This PR (HEAD: b19f271) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/go/+/199505 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Gobot Gobot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
Within the next week or so, a maintainer will review your change and provide
feedback. See https://golang.org/doc/contribute.html#review for more info and
tips to get your patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

During May-July and Nov-Jan the Go project is in a code freeze, during which
little code gets reviewed or merged. If a reviewer responds with a comment like
R=go1.11, it means that this CL will be reviewed as part of the next development
cycle. See https://golang.org/s/release for more details.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/199505.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Agniva De Sarker:

Patch Set 1: Code-Review-2

Hi Xiaoran,

This CL adds new public API. We follow the proposal process (https://golang.org/s/proposal) which needs to be discussed and approved first, and then you can send the change.

I would request you to file a github issue first outlining why you need this change and why this needs to be in the standard library. Once accepted, we can work on the review. Till then, I will mark it as -2 to prevent accidental submission.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/199505.
After addressing review feedback, remember to publish your drafts!

[fanfuxiaoran]

Have created a issue for this pr:
#34764

[fanfuxiaoran]

#34764

[bradfitz]

Closing per comments on https://go-review.googlesource.com/c/go/+/199505