Fix flaky UkmBrowserTest.EvictObsoleteSources

The browser test UkmBrowserTest.EvictObsoleteSources checks that UKM sources id are properly marked as obsolete and deleted by navigating to and leaving a few example sites, and it began to fail recently due to external change in one of the sites used in the test case. This is because source ids in the tests were obtained from web contents, which could differ from the navigation source id, for example if the site executes a same-document navigation (e.g. history.pushState/replaceState) in the case of https://www.google.com used in the test (https://screenshot.googleplex.com/xofrBc6JHB8.png).

This CL updates the test to get the source id associated to the last committed navigation from the navigation handle instead, which is consistent with the id being marked by SourceUrlRecorderWebContentsObserver::DidFinishNavigation that we aim to test.
https://cs.chromium.org/chromium/src/components/ukm/content/source_url_recorder.cc?type=cs&q=+MarkSourceForDeletion&g=0&l=237
This also changes to use an embedded test server to not depend on external content anymore.

Bug: 1004296
Change-Id: I08d7f225588598655dd946f8661d32a8dbdf53ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929018Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Yue Ru Sun <yrsun@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718304}

chrome/browser/metrics/ukm_browsertest.cc

@@ -55,6 +55,7 @@
 #include "services/network/test/test_network_quality_tracker.h"
 #include "third_party/metrics_proto/ukm/report.pb.h"
 #include "third_party/zlib/google/compression_utils.h"
+#include "url/url_constants.h"
 
 #if BUILDFLAG(ENABLE_DICE_SUPPORT)
 #include "chrome/browser/signin/scoped_account_consistency.h"
@@ -1021,21 +1022,38 @@ INSTANTIATE_TEST_SUITE_P(UkmConsentParamBrowserTests,
 // Verify that sources kept alive in-memory will be discarded by UKM service in
 // one reporting cycle after the web contents are destroyed when the tab is
 // closed or when the user navigated away in the same tab.
-// Disabled as per crbug.com/1004296.
-IN_PROC_BROWSER_TEST_F(UkmBrowserTest, DISABLED_EvictObsoleteSources) {
+IN_PROC_BROWSER_TEST_F(UkmBrowserTest, EvictObsoleteSources) {
   MetricsConsentOverride metrics_consent(true);
   Profile* profile = ProfileManager::GetActiveUserProfile();
   std::unique_ptr<ProfileSyncServiceHarness> harness =
       EnableSyncForProfile(profile);
   Browser* sync_browser = CreateBrowser(profile);
+  ASSERT_TRUE(embedded_test_server()->Start());
 
-  // Navigate to a URL in a new tab.
-  AddTabAtIndexToBrowser(sync_browser, 1, GURL("https://www.chromium.org"),
-                         ui::PAGE_TRANSITION_TYPED, true);
-  ukm::SourceId source_id1 = ukm::GetSourceIdForWebContentsDocument(
-      sync_browser->tab_strip_model()->GetWebContentsAt(1));
+  ukm::SourceId source_id1 = ukm::kInvalidSourceId;
   ukm::SourceId source_id2 = ukm::kInvalidSourceId;
 
+  const std::vector<GURL> test_urls = {
+      embedded_test_server()->GetURL("/title1.html"),
+      embedded_test_server()->GetURL("/title2.html"),
+      embedded_test_server()->GetURL("/title3.html")};
+
+  // Open a blank new tab.
+  AddTabAtIndexToBrowser(sync_browser, 1, GURL(url::kAboutBlankURL),
+                         ui::PAGE_TRANSITION_TYPED, true);
+  // Gather source id from the NavigationHandle assigned to navigations that
+  // start with the expected URL.
+  content::NavigationHandleObserver tab_1_observer(
+      sync_browser->tab_strip_model()->GetActiveWebContents(), test_urls[0]);
+  // Navigate to a test URL in this new tab.
+  ui_test_utils::NavigateToURL(sync_browser, test_urls[0]);
+  // Get the source id associated to the last committed navigation, which could
+  // differ from the id from WebContents for example if the site executes a
+  // same-document navigation (e.g. history.pushState/replaceState). This
+  // navigation source id is the one marked as obsolete by UKM recorder.
+  source_id1 = ukm::ConvertToSourceId(tab_1_observer.navigation_id(),
+                                      ukm::SourceIdType::NAVIGATION_ID);
+
   // The UKM report contains this newly-created source.
   BuildAndStoreUkmLog();
   ukm::Report report = GetUkmReport();
@@ -1048,11 +1066,14 @@ IN_PROC_BROWSER_TEST_F(UkmBrowserTest, DISABLED_EvictObsoleteSources) {
   EXPECT_TRUE(has_source_id1);
   EXPECT_FALSE(has_source_id2);
 
-  // Navigate to a URL in another new tab.
-  AddTabAtIndexToBrowser(sync_browser, 2, GURL("https://www.google.com"),
+  // Navigate to another URL in a new tab.
+  AddTabAtIndexToBrowser(sync_browser, 2, GURL(url::kAboutBlankURL),
                          ui::PAGE_TRANSITION_TYPED, true);
-  source_id2 = ukm::GetSourceIdForWebContentsDocument(
-      sync_browser->tab_strip_model()->GetWebContentsAt(2));
+  content::NavigationHandleObserver tab_2_observer(
+      sync_browser->tab_strip_model()->GetActiveWebContents(), test_urls[1]);
+  ui_test_utils::NavigateToURL(sync_browser, test_urls[1]);
+  source_id2 = ukm::ConvertToSourceId(tab_2_observer.navigation_id(),
+                                      ukm::SourceIdType::NAVIGATION_ID);
 
   // The next report should again contain source 1 because the tab is still
   // alive, and also source 2 associated to the new tab that has just been
@@ -1087,7 +1108,7 @@ IN_PROC_BROWSER_TEST_F(UkmBrowserTest, DISABLED_EvictObsoleteSources) {
 
   // Navigate to a new URL in the current tab, this will mark source 2 that was
   // in the current tab as obsolete.
-  ui_test_utils::NavigateToURL(sync_browser, GURL("https://www.wikipedia.org"));
+  ui_test_utils::NavigateToURL(sync_browser, test_urls[2]);
 
   // The previous report was the last one that could potentially contain entries
   // for source 1. Source 1 is thus no longer included in future reports. This