Expose kv-storage built-in module only on SecureContexts

This CL adds actual restriction in Blink implementation.

This CL also modifies tests and expectations to match with
the current Blink built-in/import maps infra.

A subtest in WPT test `import-statement.html` is failing
because the current Blink implementation is based on
pre-import-map spec and thus
importing unavailable built-in causes fetch error.
See 'import 'std:nonexistent';' row of
WICG/import-maps#159.

Bug: 977470
Change-Id: I107f60ed95e1f91d62f468c29c5d741eef13f4f9

kv-storage/secure-context/import-maps.html

@@ -15,7 +15,7 @@
 <script type="importmap">
 {
   "imports": {
-    "std:kv-storage": [
+    "./resources/dummy-module.js": [
       "std:kv-storage",
       "./resources/dummy-module.js"
     ]
@@ -25,7 +25,7 @@
 
 <script type="module">
 promise_test(async () => {
-  const result = await import("std:kv-storage");
-  assert_equals(namespaceObj.myExport, "not the real KV storage");
+  const result = await import("./resources/dummy-module.js");
+  assert_equals(result.myExport, "not the real KV storage");
 });
 </script>

kv-storage/secure-context/import-statement.html

@@ -13,13 +13,14 @@
   assert_false(self.isSecureContext, "This test must run in a non-secure context");
 }, "Prerequisite check");
 
-async_test(t => {
-  window.addEventListener("error", t.step_func_done(errorEvent => {
-    assert_equals(errorEvent.error.constructor, TypeError, "Must trigger a TypeError");
-  }, { once: true }));
-});
+const t = async_test('Static import kv-storage in non-secure context');
+
+window.addEventListener("error", t.step_func_done(errorEvent => {
+  assert_equals(errorEvent.error.constructor, TypeError, "Must trigger a TypeError");
+}, { once: true }));
 </script>
 
-<script type="module">
+<script type="module"
+  onerror="t.unreached_func('script error event should not be fired')()">
 import "std:kv-storage";
 </script>