Create merge base for git.

Create merge base for git.

Release 1.55.0

[SVN r86621]

Release 1.54.0

[SVN r84923]

Release 1.54.0 beta1

[SVN r84619]

Release 1.53.0

[SVN r82734]

Release 1.52.0

[SVN r81201]

Release 1.51.0

[SVN r80098]

Release 1.50.0

[SVN r79156]

Release 1.50.0 beta 1

[SVN r78831]