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/loop_with_continuing.wgsl b/test/loops/loop_with_continuing.wgsl
new file mode 100644
index 0000000..a406853
--- /dev/null
+++ b/test/loops/loop_with_continuing.wgsl
@@ -0,0 +1,12 @@
+fn f() -> i32 {
+    var i : i32;
+    loop {
+        if (i > 4) {
+            return i;
+        }
+        continuing {
+            i = i + 1;
+        }
+    }
+    return 0;
+}