tree f8c853f98ba4e897b1357aaa59a0dfc14cefc946
parent 91fc61a883612e30ca2dd2471245817f400b29cf
author Zhen Chen <czhen@google.com> 1476397261 -0700
committer Zhen Chen <czhen@google.com> 1476811631 -0700

Fix project ordering bug in submodule subscription

The initial idea for sorting project is relying on the sorted branches.
However, sorted branches does not always guarantee a valid order for
projects. For example:

Scenario: super.master -> sub.master(C1) and super.dev -> sub.dev(C2)
When change C1 and C2 are submitted together, there are multiple
possible sorted branches orders, here are two example.

1. sub.master - super.master - sub.dev - super.dev
2. sub.master - sub.dev - super.master - super.dev

Only #2 can derive a valid project order and #1 will give us a project
circular subscription exception.

Rewrite the project sorting algorithm:
1. find all *superbranches* (branches that have subscriptions) in a
superproject
2. find all submodule projects for these superbranches
Recursively doing 1,2 until there is no superbranches, and add that
project to the sorted project list.

Tests are also added for the example.

Change-Id: Ia8e794f630ce303320c242fb9922d831f502c186