Update test/tint/array to store results

This CL updates the `test/tint/array` tests to make sure the results
are stored back into a storage variable. Also make sure each test has
an entry point.

Change-Id: I8a87129c22ed56bdbcecf69464aa03e9ce387659
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/164580
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: dan sinclair <dsinclair@chromium.org>
diff --git a/test/tint/array/assign_to_workgroup_var.wgsl b/test/tint/array/assign_to_workgroup_var.wgsl
index 74f3e67..356ca0e 100644
--- a/test/tint/array/assign_to_workgroup_var.wgsl
+++ b/test/tint/array/assign_to_workgroup_var.wgsl
@@ -50,3 +50,9 @@
   var src_nested : array<array<array<i32, 2>, 3>, 4>;
   dst_nested = src_nested;
 }
+
+@compute @workgroup_size(1)
+fn main() {
+  let val = ArrayType();
+  foo(val);
+}