Add a sample file exercising contiguous item logic

sample_files/contiguous_after.js

@@ -0,0 +1,7 @@
+// There are multiple possible diffs here, but we want to prefer
+// showing A and B on the same line.
+var x = [
+  "A", "B",
+  "A", "B",
+  "C", "D",
+];

sample_files/contiguous_before.js

@@ -0,0 +1,5 @@
+
+var x = [
+  "A", "B",
+  "C", "D",
+];