Remove Guava from GWT build

This is the only reference to Guava code in the GWT UI build.
Convert back to normal Java usage so Guava is not required as
a dependency for the UI build.

Change-Id: I7689cb1ee97ca855f29d76f25d9e5f8a34a8bd88
diff --git a/gerrit-common/src/main/java/com/google/gerrit/common/data/GarbageCollectionResult.java b/gerrit-common/src/main/java/com/google/gerrit/common/data/GarbageCollectionResult.java
index 93f283b..e4d7b80 100644
--- a/gerrit-common/src/main/java/com/google/gerrit/common/data/GarbageCollectionResult.java
+++ b/gerrit-common/src/main/java/com/google/gerrit/common/data/GarbageCollectionResult.java
@@ -14,16 +14,16 @@
 
 package com.google.gerrit.common.data;
 
-import com.google.common.collect.Lists;
 import com.google.gerrit.reviewdb.client.Project;
 
+import java.util.ArrayList;
 import java.util.List;
 
 public class GarbageCollectionResult {
   protected List<Error> errors;
 
   public GarbageCollectionResult() {
-    errors = Lists.newArrayList();
+    errors = new ArrayList<Error>();
   }
 
   public void addError(Error e) {