[WPT Export] Add merge_method: rebase to WPTGitHub.merge_pull_request

[WPT Export] Add merge_method: rebase to WPTGitHub.merge_pull_request

BUG=682883
Review-Url: https://codereview.chromium.org/2658713002
Cr-Commit-Position: refs/heads/master@{#446244}
Committed: https://chromium.googlesource.com/chromium/src/+/e0a2ec09d1087b572e70002fce286231c0fef823

[jeffcarp, 2017-01-26 00:03:53]

jeffcarp@chromium.org changed reviewers:
+ qyearsley@chromium.org

[qyearsley, 2017-01-26 00:05:17]

lgtm

[jeffcarp, 2017-01-26 03:59:52]

The CQ bit was checked by jeffcarp@chromium.org

[commit-bot: I haz the power, 2017-01-26 04:00:23]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-26 05:51:40]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1485403192776270, "parent_rev":
"94ca0ca859f45ecb6d3d26704c9501d965fadf9f", "commit_rev":
"e0a2ec09d1087b572e70002fce286231c0fef823"}

[commit-bot: I haz the power, 2017-01-26 05:52:11]

Description was changed from

==========
[WPT Export] Add merge_method: rebase to WPTGitHub.merge_pull_request

BUG=682883
==========

to

==========
[WPT Export] Add merge_method: rebase to WPTGitHub.merge_pull_request

BUG=682883

Review-Url: https://codereview.chromium.org/2658713002
Cr-Commit-Position: refs/heads/master@{#446244}
Committed:
https://chromium.googlesource.com/chromium/src/+/e0a2ec09d1087b572e70002fce28...
==========

[commit-bot: I haz the power, 2017-01-26 05:52:12]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/e0a2ec09d1087b572e70002fce28...