As an example, if there is commit C (300 days old) in dev branch. Later dev is merged into upstream-master as commit M (2 days old).

Before this change, the updater will say "2 commits (300 days) behind" because both C and M is not in master.

After this change, it will say "1 commit (2 days) behind", which makes more sense.

(This change raises error when there's no merge base between upstream and master. But I think it is expected)

Test: updater.sh check googletest
Change-Id: I963b378e61677c1f6ea13af0d0f558846040b840

This change computes edit distant between old url and each of new urls.
And use the url most like previous one.

Test: update any library
Change-Id: I959a22168652c7543da2cdb29d36a1d061ade7e9

Add the support to check how far a project is behind upstream git.

Still need to manually run git merge. But this tool can help update
METADATA. :)

Test: ./updater.sh update perf_data_converter
Change-Id: Ic46a0eb723ae22f0fc7d61a67a14299761b564a4