Local NTP tests: Wait for MV items to load before running tests

Some tests depend on the availability of the default prepopulated MV
items from TopSites. Since TopSites loads asynchronously, it's possible
that these items aren't available when a test runs, which manifests as
test flakiness. This CL adds an explicit wait before running the tests.

Bug: 793818
Change-Id: Iabb745f038bc44fc2d46ab263fe944b6e996412f
Reviewed-on: https://chromium-review.googlesource.com/831524Reviewed-by: Chris Pickel <sfiera@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524681}

chrome/browser/ui/search/local_ntp_browsertest.cc

@@ -55,14 +55,69 @@ namespace {
 // default TopSites tiles (see history::PrepopulatedPage).
 const int kDefaultMostVisitedItemCount = 2;
 
-class LocalNTPTest : public InProcessBrowserTest {
+class TestMostVisitedObserver : public InstantServiceObserver {
  public:
-  LocalNTPTest() {}
+  explicit TestMostVisitedObserver(InstantService* service)
+      : service_(service), expected_count_(0) {
+    service_->AddObserver(this);
+  }
+
+  ~TestMostVisitedObserver() override { service_->RemoveObserver(this); }
+
+  void WaitForNumberOfItems(size_t count) {
+    DCHECK(!quit_closure_);
+
+    expected_count_ = count;
+
+    if (items_.size() == count) {
+      return;
+    }
+
+    base::RunLoop run_loop;
+    quit_closure_ = run_loop.QuitClosure();
+    run_loop.Run();
+  }
 
  private:
-  void SetUp() override {
+  void ThemeInfoChanged(const ThemeBackgroundInfo&) override {}
+
+  void MostVisitedItemsChanged(
+      const std::vector<InstantMostVisitedItem>& items) override {
+    items_ = items;
+
+    if (quit_closure_ && items_.size() == expected_count_) {
+      std::move(quit_closure_).Run();
+      quit_closure_.Reset();
+    }
+  }
+
+  InstantService* const service_;
+
+  std::vector<InstantMostVisitedItem> items_;
+
+  size_t expected_count_;
+  base::OnceClosure quit_closure_;
+};
+
+class LocalNTPTest : public InProcessBrowserTest {
+ public:
+  LocalNTPTest() {
     feature_list_.InitAndEnableFeature(features::kUseGoogleLocalNtp);
-    InProcessBrowserTest::SetUp();
+  }
+
+ private:
+  void SetUpOnMainThread() override {
+    // Some tests depend on the prepopulated most visited tiles coming from
+    // TopSites, so make sure they are available before running the tests.
+    // (TopSites is loaded asynchronously at startup, so without this, there's
+    // a chance that it hasn't finished and we receive 0 tiles.)
+    InstantService* instant_service =
+        InstantServiceFactory::GetForProfile(browser()->profile());
+    TestMostVisitedObserver mv_observer(instant_service);
+    // Make sure the observer knows about the current items. Typically, this
+    // gets triggered by navigating to an NTP.
+    instant_service->UpdateMostVisitedItemsInfo();
+    mv_observer.WaitForNumberOfItems(kDefaultMostVisitedItemCount);
   }
 
   base::test::ScopedFeatureList feature_list_;
@@ -176,50 +231,6 @@ IN_PROC_BROWSER_TEST_F(LocalNTPTest, EmbeddedSearchAPIExposesStaticFunctions) {
   }
 }
 
-class TestMostVisitedObserver : public InstantServiceObserver {
- public:
-  explicit TestMostVisitedObserver(InstantService* service)
-      : service_(service), expected_count_(0) {
-    service_->AddObserver(this);
-  }
-
-  ~TestMostVisitedObserver() override { service_->RemoveObserver(this); }
-
-  void WaitForNumberOfItems(size_t count) {
-    DCHECK(!quit_closure_);
-
-    expected_count_ = count;
-
-    if (items_.size() == count) {
-      return;
-    }
-
-    base::RunLoop run_loop;
-    quit_closure_ = run_loop.QuitClosure();
-    run_loop.Run();
-  }
-
- private:
-  void ThemeInfoChanged(const ThemeBackgroundInfo&) override {}
-
-  void MostVisitedItemsChanged(
-      const std::vector<InstantMostVisitedItem>& items) override {
-    items_ = items;
-
-    if (quit_closure_ && items_.size() == expected_count_) {
-      std::move(quit_closure_).Run();
-      quit_closure_.Reset();
-    }
-  }
-
-  InstantService* const service_;
-
-  std::vector<InstantMostVisitedItem> items_;
-
-  size_t expected_count_;
-  base::OnceClosure quit_closure_;
-};
-
 IN_PROC_BROWSER_TEST_F(LocalNTPTest, EmbeddedSearchAPIEndToEnd) {
   content::WebContents* active_tab =
       local_ntp_test_utils::OpenNewTab(browser(), GURL("about:blank"));