CookieStore: Add validation behavior for __Host- prefixed cookies

This change adds the following checks for "__Host-" prefixed cookies:

1. Disallows overwriting with an explicit domain
2. Disallows non "/" path

This behavior is mentioned in the spec here [1].
Creating a cookie that violates this will cause a crash without
this change.

[1] https://wicg.github.io/cookie-store/#prefixes

Change-Id: I20968f11759019921aa7a6b37602878a17b091ff

cookie-store/cookieStore_special_names.tentative.https.any.js

@@ -32,3 +32,24 @@
       `Deleting ${prefix} cookies should not fail in secure context`);
   }, `cookieStore.delete with ${prefix} name on secure origin`);
 });
+
+promise_test(async testCase => {
+  const currentUrl = new URL(self.location.href);
+  const currentDomain = currentUrl.hostname;
+  await promise_rejects_js(testCase, TypeError,
+      cookieStore.set('__Host-cookie-name', 'cookie-value', {
+        domain: currentDomain
+      }));
+}, 'cookieStore.set with __Host- prefix and a domain option');
+
+promise_test(async testCase => {
+  await cookieStore.set('__Host-cookie-name', 'cookie-value', { path: "/" });
+
+  assert_equals(
+      (await cookieStore.get(`__Host-cookie-name`)).value, "cookie-value");
+
+  await promise_rejects_js(testCase, TypeError,
+      cookieStore.set('__Host-cookie-name', 'cookie-value', {
+        path: "/path"
+      }));
+}, 'cookieStore.set with __Host- prefix a path option');