[Prerender] Remove Prerender metrics observer test.

This functionality is covered in PageLoadMetricsBrowserTest for the most
part, and this CL adds another metrics check after which the
PrerenderBrowserTest test can be removed.

Bug: 898955
Change-Id: Ic482516272d59f3c47b807a57e5d108b93c9c7e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2239839Reviewed-by: Egor Pasko <pasko@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Mugdha Lakhani <nator@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777301}

chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc

@@ -1119,6 +1119,8 @@ IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest,
       "Prerender.none_PrefetchTTFCP.Reference.NoStore.Visible", 0);
   histogram_tester_.ExpectTotalCount(
       "Prerender.none_PrefetchTTFCP.Reference.Cacheable.Visible", 1);
+  histogram_tester_.ExpectTotalCount(
+      "PageLoad.PaintTiming.ParseStartToFirstContentfulPaint", 1);
 }
 
 IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest,

chrome/browser/prerender/prerender_browsertest.cc

@@ -913,28 +913,6 @@ class PrerenderBrowserTest : public test_utils::PrerenderInProcessBrowserTest {
   std::unique_ptr<content::URLLoaderInterceptor> interceptor_;
 };
 
-// Checks that the correct page load metrics observers are produced without a
-// prerender.
-IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, PageLoadMetricsSimple) {
-  // The prefetch page is used as a simple page with a nonempty layout; no
-  // prefetching is performed.
-  test_utils::FirstContentfulPaintManagerWaiter* simple_fcp_waiter =
-      test_utils::FirstContentfulPaintManagerWaiter::Create(
-          GetPrerenderManager());
-  ui_test_utils::NavigateToURL(
-      current_browser(), src_server()->GetURL("/prerender/prefetch_page.html"));
-  simple_fcp_waiter->Wait();
-
-  histogram_tester().ExpectTotalCount(
-      "Prerender.none_PrefetchTTFCP.Reference.Cacheable.Visible", 1);
-  histogram_tester().ExpectTotalCount(
-      "PageLoad.PaintTiming.ParseStartToFirstContentfulPaint", 1);
-
-  // Histogram only emitted during a prerender, which should not happen here.
-  histogram_tester().ExpectTotalCount(
-      "Prerender.websame_PrefetchTTFCP.Warm.Cacheable.Visible", 0);
-}
-
 // Checks that pending prerenders which are canceled before they are launched
 // never get started.
 IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, PrerenderPageRemovesPending) {