[kudu-CR] schema: add is deleted virtual column

["Adar Dembo (Code Review)" <ge...@cloudera.org>]

Hello Mike Percy, Kudu Jenkins, Grant Henke, Todd Lipcon, 

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/10968

to look at the new patch set (#3).

Change subject: schema: add is_deleted virtual column
......................................................................

schema: add is_deleted virtual column

This patch introduces a very basic concept of a "virtual column", defined as
a static column with a name, type, and defaults. A Kudu subsystem that
wishes to interact with a virtual column needs to first figure out if the
projection includes it (via ColumnSchema::Equals()). When projected, the
virtual column's data will be entirely default; it's the subsystem's
responsibility to fill in something meaningful afterwards.

This first cut is hardly robust. It remains to be seen how usable this
bare-bones abstraction will be; so far it's sufficient for the MemRowSet.

Change-Id: I56eb1d44ba8bfbd76d8bb794b8076b695782939e
---
M src/kudu/common/schema.cc
M src/kudu/common/schema.h
M src/kudu/master/catalog_manager.cc
M src/kudu/master/master-test.cc
4 files changed, 49 insertions(+), 4 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/68/10968/3
-- 
To view, visit http://gerrit.cloudera.org:8080/10968
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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I56eb1d44ba8bfbd76d8bb794b8076b695782939e
Gerrit-Change-Number: 10968
Gerrit-PatchSet: 3
Gerrit-Owner: Adar Dembo <ad...@cloudera.com>
Gerrit-Reviewer: Grant Henke <gr...@apache.org>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Mike Percy <mp...@apache.org>
Gerrit-Reviewer: Todd Lipcon <to...@apache.org>