FasterLocationReload: use ReloadMainResource for JS exposed reloads

third_party/WebKit/LayoutTests/http/tests/cache/location-reload.html

+<!DOCYUPE html>
+<h1>random</h1>
+<script src="../resources/testharness.js"></script>
+<script src="../resources/testharnessreport.js"></script>
+<script>
+
+async_test(t => {
+  const passMessage = "PASS";
+  const readyMessage = "READY";
+  let expectedMessage = readyMessage;
+  let testWindow = null;
+  let messageCount = 0;
+
+  // Test will run on testWindow that is opened below.
+  // This page just received messages to confirm if tests run expectedly.
+  window.addEventListener("message", e => {
+    t.step(() => {
+      // Check if messages are received in an expected order.
+      assert_equals(e.data, expectedMessage, "received message is " + e.data);
+
+      // If all tests pass, "PASS" will be received.
+      if (e.data == passMessage) {
+        t.done();
+      } else {
+        // Will receive "READY" twice because of a reload, then receive "PASS".
+        // Update expectedMessage as it will.
+        messageCount++;
+        if (messageCount == 2)
+          expectedMessage = passMessage;
+
+        // Send back "START" message for "READY".
+        assert_class_string(testWindow, "Window", "testWindow is invalid");
+        testWindow.postMessage("START", location.origin);
+      }
+    });
+  }, false);

[kouhei (in TOK), 2016/12/14 10:57:41]

Try addEventListener("msg", e => {...},  {once: true}) instead of
expectedMessage?

[Takashi Toyoshima, 2016/12/14 12:31:10]

Done.

+
+  // Start a test in a dedicated window because we can not track navigations
+  // within a test harness.
+  t.step(() => {
+    testWindow = open("./resources/location-reload-window.html", "testWindow");
+    assert_class_string(testWindow, "Window", "window.open() fails");

[kouhei (in TOK), 2016/12/14 10:57:41]

s/fails/failed

[Takashi Toyoshima, 2016/12/14 12:31:10]

Done.

+  });
+}, "Test location.reload() cache behaviors");
+</script>