Ensure all content_browsertests call the host resolver in SetUpOnMainThread and not after.

content/browser/web_contents/opened_by_dom_browsertest.cc

Index: content/browser/web_contents/opened_by_dom_browsertest.cc
diff --git a/content/browser/web_contents/opened_by_dom_browsertest.cc b/content/browser/web_contents/opened_by_dom_browsertest.cc
index 699121da96fa3502a995b1a1f583153db0fdf2ab..0f506b50b4101fa5f3f40f52059681a522bef7d5 100644
--- a/content/browser/web_contents/opened_by_dom_browsertest.cc
+++ b/content/browser/web_contents/opened_by_dom_browsertest.cc
@@ -47,6 +47,10 @@ class OpenedByDOMTest : public ContentBrowserTest {
     IsolateAllSitesForTesting(command_line);
   }
 
+  void SetUpOnMainThread() override {
+    host_resolver()->AddRule("*", "127.0.0.1");
+  }
+
   bool AttemptCloseFromJavaScript(WebContents* web_contents) {
     CloseTrackingDelegate close_tracking_delegate;
     WebContentsDelegate* old_delegate = web_contents->GetDelegate();
@@ -114,7 +118,6 @@ IN_PROC_BROWSER_TEST_F(OpenedByDOMTest, Popup) {
 // Tests that window.close() works in a popup window that has navigated a few
 // times and swapped processes.
 IN_PROC_BROWSER_TEST_F(OpenedByDOMTest, CrossProcessPopup) {
-  host_resolver()->AddRule("*", "127.0.0.1");
   ASSERT_TRUE(embedded_test_server()->Start());
 
   GURL url1 = embedded_test_server()->GetURL("/site_isolation/blank.html?1");