Protoc, C++ runtime and Java runtime are updated to v3.0.0-beta-1, other
languages are updated to v3.0.0-alpha-4.

default configuration. In default configuration, maven needs webdav for
deployment, which cannot be found in central repository.

Upstreamed from Another Place (cr/57247854).

Change-Id: I2aaf59544c0f5ae21a51891d8a5eeda1dc722c90

https://android-review.googlesource.com/#/c/67890/ removed field
initialization from the ctor, making it just call clear() instead.

When I added the generate_clear option back (as part of the reftypes
compat mode) in https://android-review.googlesource.com/#/c/109530/,
I forgot to ensure that what clear() used to do was inlined in the
constructor.

This change fixes NPEs that are happening for users of
reftypes_compat_mode who rely on unset repeated fields being empty
arrays rather than null.

Change-Id: Idb58746c60f4a4054b7ebb5c3b0e76b16ff88184

Change-Id: I885b561c85325db05595f0d86338dcd7c06cf058

Change-Id: I33479e529b060e4fed532a827a386d3baecc835e

Change-Id: Icecb25db34ae5e6d5142a2d75ca7216ba018abb2