Document the 'Buck Exit Criteria'

This came from the repo-discuss mailing list thread[1] and is a
summary of the major criteria that has been proposed. As issues
are resolved we will delete these entries from the documentation,
until either the section itself can be removed, or we have reached
September 1st 2013 (~3 months) and the build issue can be revisited.

[1] https://groups.google.com/d/msg/repo-discuss/gt2Oeb9LkeI/xsX5HKMH5QoJ

Change-Id: Id9b7dacb75fe8bd74d45e9ed141ac4799314a331

Documentation/dev-buck.txt

@@ -133,6 +133,57 @@ Force a download of dependency JARs by building the `download` target:
 ----
 
 
+Build Process Switch Exit Criteria
+----------------------------------
+
+The switch to Buck is an experimental process. Buck will become the
+primary build for Gerrit (and link:dev-maven.html[Maven support]
+removed) only when the following conditions are met.
+
+1. Windows support.
++
+Facebook has an intern who will be working on this (summer 2013).
+
+2. Bootstrap and stable version support.
++
+From a fresh Gerrit clone on a machine without Buck (but with some
+reasonable subset of Buck's dependencies, e.g. Python 2.7), a new
+Gerrit developer should be able to set up and start building with
+Buck by running approximately one command. There should also be some
+idea of a "stable" version of Buck, even if we just tie our build
+to specific known-good SHAs. Binary distributions are another plus,
+which I believe the Buck team has planned.
+
+3. Eclipse support.
++
+Much of this is already there. The build needs to be at least as
+reliable as it is under Maven. (This is kind of a low bar, due to
+issues like Maven not handling generated Prolog source files or
+recompiling the GWT source.)
+
+4. Build without Internet access.
++
+Currently dependencies are downloaded directly from Maven Central
+and Gerrit's Google Cloud Storage bucket. In some environments
+build systems do not have direct network access. It must be possible
+for a developer to swap out the upstream Maven Central URL with an
+internal Maven mirror, or to supply all of the JARs themselves.
+
+5. Shawn's Buck fork merged upstream.
++
+Shawn has a link:https://gerrit.googlesource.com/buck/+log/github-master..master[fork of Buck]
+with some patches necessary to build Gerrit and run its unit tests.
+These patches (or their equivalents) must be in the upstream Buck tree.
+
+6. Fix all incidental issues.
++
+Things come up that don't work. Martin just ran out of file
+descriptors, which sounds like an upstream bug.
++
+There should be a consensus that new bugs like this in upstream
+Buck are not constantly being introduced.
+
+
 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]