Make com.facebook.buck.util.concurrent.MoreExecutors available to our JUnitRunner.

Summary:
BuckBlockJUnit4ClassRunner contains some copy/paste code from MoreExecutors because
our JUnit runner uses a restricted classpath. This diff refactors things to share
the MoreExecutors code with our JUnitRunner.

Also remove duplicate documentation in BuckBlockJUnit4ClassRunner.

Test Plan: Sandcastle builds.

build.xml

diff --git a/build.xml b/build.xml
index 7e075b7..7520c21 100644
--- a/build.xml
+++ b/build.xml
@@ -7,7 +7,6 @@
   <property name="lib.dir" value="${basedir}/lib" />
   <property name="third-party.dir" value="${basedir}/third-party" />
   <property name="build.dir" value="${basedir}/build" />
-  <property name="testrunner.src.dir" value="${src.dir}/com/facebook/buck/junit/" />
   <property name="testrunner.classes.dir" value="${build.dir}/testrunner/classes" />
   <property name="abi_processor.src.dir" value="${src.dir}/com/facebook/buck/java/abi/" />
   <property name="abi_processor.classes.dir" value="${build.dir}/abi_processor/classes" />
@@ -90,7 +89,8 @@
 
   <target name="compile-testrunner" depends="checkversion">
     <mkdir dir="${testrunner.classes.dir}" />
-    <javac srcdir="${testrunner.src.dir}"
+    <javac srcdir="${src.dir}"
+           includes="com/facebook/buck/junit/**,src/com/facebook/buck/util/concurrent/MoreExecutors.java"
            destdir="${testrunner.classes.dir}"
            classpathref="junit"
            debug="on"

src/com/facebook/buck/junit/BUCK

diff --git a/src/com/facebook/buck/junit/BUCK b/src/com/facebook/buck/junit/BUCK
index d91e09c..87e05ea 100644
--- a/src/com/facebook/buck/junit/BUCK
+++ b/src/com/facebook/buck/junit/BUCK
@@ -6,6 +6,7 @@
     # Java API. The objective is to limit the set of files added to the ClassLoader that runs the
     # test, as not to interfere with the results of the test.
     '//lib:junit',
+    '//src/com/facebook/buck/util/concurrent:concurrent_for_junit_runner',
   ],
   visibility = [
     '//test/com/facebook/buck/junit:junit',

src/com/facebook/buck/junit/BuckBlockJUnit4ClassRunner.java

diff --git a/src/com/facebook/buck/junit/BuckBlockJUnit4ClassRunner.java b/src/com/facebook/buck/junit/BuckBlockJUnit4ClassRunner.java
index 5674f34..f6e8962 100644
--- a/src/com/facebook/buck/junit/BuckBlockJUnit4ClassRunner.java
+++ b/src/com/facebook/buck/junit/BuckBlockJUnit4ClassRunner.java
@@ -16,6 +16,8 @@
 
 package com.facebook.buck.junit;
 
+import com.facebook.buck.util.concurrent.MoreExecutors;
+
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.Timeout;
@@ -36,8 +38,6 @@
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
-import java.util.concurrent.LinkedBlockingQueue;
-import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 
@@ -55,15 +55,7 @@
   // Executors.newSingleThreadExecutor(). The problem with Executors.newSingleThreadExecutor() is
   // that it does not let us specify a RejectedExecutionHandler, which we need to ensure that
   // garbage is not spewed to the user's console if the build fails.
-  // Executors.newSingleThreadExecutor(). The problem with Executors.newSingleThreadExecutor() is
-  // that it does not let us specify a RejectedExecutionHandler, which we need to ensure that
-  // garbage is not spewed to the user's console if the build fails.
-  private final ExecutorService executor = new ThreadPoolExecutor(
-        /* corePoolSize */ 1,
-        /* maximumPoolSize */ 1,
-        /* keepAliveTime */ 0L, TimeUnit.MILLISECONDS,
-        /* workQueue */ new LinkedBlockingQueue<Runnable>(),
-        /* handler */ new ThreadPoolExecutor.DiscardPolicy());
+  private final ExecutorService executor = MoreExecutors.newSingleThreadExecutor();
 
   private final long defaultTestTimeoutMillis;
 

src/com/facebook/buck/util/concurrent/BUCK

diff --git a/src/com/facebook/buck/util/concurrent/BUCK b/src/com/facebook/buck/util/concurrent/BUCK
index 92540c6..8ef25f2 100644
--- a/src/com/facebook/buck/util/concurrent/BUCK
+++ b/src/com/facebook/buck/util/concurrent/BUCK
@@ -7,3 +7,13 @@
   visibility = ['PUBLIC'],
 )
 
+java_library(
+  name = 'concurrent_for_junit_runner',
+  srcs = [ 'MoreExecutors.java' ],
+  deps = [
+    # IMPORTANT! This list is to remain empty. See src/com/facebook/buck/junit/BUCK.
+  ],
+  visibility = [
+    '//src/com/facebook/buck/junit:junit',
+  ],
+)