test: Add loop test cases

Bug: tint:833
Bug: tint:914
Change-Id: Ieb34c734ad08c632c8d4e6152d856ec28f35cf85
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/55249
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
diff --git a/test/loops/nested_loops.wgsl.expected.wgsl b/test/loops/nested_loops.wgsl.expected.wgsl
new file mode 100644
index 0000000..048cd04
--- /dev/null
+++ b/test/loops/nested_loops.wgsl.expected.wgsl
@@ -0,0 +1,17 @@
+fn f() -> i32 {
+  var i : i32;
+  var j : i32;
+  loop {
+    i = (i + 1);
+    if ((i > 4)) {
+      return 1;
+    }
+    loop {
+      j = (j + 1);
+      if ((j > 4)) {
+        return 2;
+      }
+    }
+  }
+  return 0;
+}