Override SetUpOnMainThread instead of PreRunTestOnMainThread in two weblayer browertests.

Per the comments in BrowserTestBase, PreRunTestOnMainThread is meant to be inherited just by test harnesses.

Change-Id: I8e3e0e20589219f4a1561ca194ea3d73c7378b2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980983Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728003}

weblayer/browser/safe_browsing/safe_browsing_browsertest.cc

@@ -79,8 +79,7 @@ class SafeBrowsingBrowserTest : public WebLayerBrowserTest {
   ~SafeBrowsingBrowserTest() override = default;
 
   // WebLayerBrowserTest:
-  void PreRunTestOnMainThread() override {
-    WebLayerBrowserTest::PreRunTestOnMainThread();
+  void SetUpOnMainThread() override {
     NavigateAndWaitForCompletion(GURL("about:blank"), shell());
     safe_browsing::SafeBrowsingApiHandler::SetInstance(fake_handler_.get());
     ASSERT_TRUE(embedded_test_server()->Start());

weblayer/browser/ssl_browsertest.cc

@@ -24,9 +24,7 @@ class SSLBrowserTest : public WebLayerBrowserTest {
   ~SSLBrowserTest() override = default;
 
   // WebLayerBrowserTest:
-  void PreRunTestOnMainThread() override {
-    WebLayerBrowserTest::PreRunTestOnMainThread();
-
+  void SetUpOnMainThread() override {
     https_server_ = std::make_unique<net::EmbeddedTestServer>(
         net::EmbeddedTestServer::TYPE_HTTPS);
     https_server_->AddDefaultHandlers(