Re-enable start up tests that were flaky on Linux

WelcomeBackStandardNoPolicy and UpdateWithTwoProfiles were disabled
because they were falky on Linux. After some minor fix, they are now
ready to be re-enabled.

BUG=379579

Change-Id: I2e2a79761b4ab6e0f5c9fb18daa3ae80ed9c282a
Reviewed-on: https://chromium-review.googlesource.com/c/1354681Reviewed-by: Tommy Martino <tmartino@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612361}

chrome/browser/ui/startup/startup_browser_creator_browsertest.cc

@@ -648,13 +648,19 @@ IN_PROC_BROWSER_TEST_F(StartupBrowserCreatorTest, PRE_UpdateWithTwoProfiles) {
   // Create two profiles.
   base::FilePath dest_path = profile_manager->user_data_dir();
 
-  Profile* profile1 = profile_manager->GetProfile(
-      dest_path.Append(FILE_PATH_LITERAL("New Profile 1")));
-  ASSERT_TRUE(profile1);
+  Profile* profile1 = nullptr;
+  Profile* profile2 = nullptr;
+  {
+    base::ScopedAllowBlockingForTesting allow_blocking;
+    profile1 = profile_manager->GetProfile(
+        dest_path.Append(FILE_PATH_LITERAL("New Profile 1")));
+    ASSERT_TRUE(profile1);
 
-  Profile* profile2 = profile_manager->GetProfile(
-      dest_path.Append(FILE_PATH_LITERAL("New Profile 2")));
-  ASSERT_TRUE(profile2);
+    profile2 = profile_manager->GetProfile(
+        dest_path.Append(FILE_PATH_LITERAL("New Profile 2")));
+    ASSERT_TRUE(profile2);
+  }
+  DisableWelcomePages({profile1, profile2});
 
   // Open some urls with the browsers, and close them.
   Browser* browser1 =
@@ -693,10 +699,7 @@ IN_PROC_BROWSER_TEST_F(StartupBrowserCreatorTest, PRE_UpdateWithTwoProfiles) {
   profile2->GetPrefs()->CommitPendingWrite();
 }
 
-// See crbug.com/376184 about improvements to this test on Mac.
-// Disabled because it's flaky. http://crbug.com/379579
-IN_PROC_BROWSER_TEST_F(StartupBrowserCreatorTest,
-                       DISABLED_UpdateWithTwoProfiles) {
+IN_PROC_BROWSER_TEST_F(StartupBrowserCreatorTest, UpdateWithTwoProfiles) {
   // Make StartupBrowserCreator::WasRestarted() return true.
   StartupBrowserCreator::was_restarted_read_ = false;
   PrefService* pref_service = g_browser_process->local_state();
@@ -707,13 +710,18 @@ IN_PROC_BROWSER_TEST_F(StartupBrowserCreatorTest,
   // Open the two profiles.
   base::FilePath dest_path = profile_manager->user_data_dir();
 
-  Profile* profile1 = profile_manager->GetProfile(
-      dest_path.Append(FILE_PATH_LITERAL("New Profile 1")));
-  ASSERT_TRUE(profile1);
+  Profile* profile1 = nullptr;
+  Profile* profile2 = nullptr;
+  {
+    base::ScopedAllowBlockingForTesting allow_blocking;
+    profile1 = profile_manager->GetProfile(
+        dest_path.Append(FILE_PATH_LITERAL("New Profile 1")));
+    ASSERT_TRUE(profile1);
 
-  Profile* profile2 = profile_manager->GetProfile(
-      dest_path.Append(FILE_PATH_LITERAL("New Profile 2")));
-  ASSERT_TRUE(profile2);
+    profile2 = profile_manager->GetProfile(
+        dest_path.Append(FILE_PATH_LITERAL("New Profile 2")));
+    ASSERT_TRUE(profile2);
+  }
 
   // Simulate a launch after a browser update.
   base::CommandLine dummy(base::CommandLine::NO_PROGRAM);
@@ -1434,13 +1442,8 @@ IN_PROC_BROWSER_TEST_F(StartupBrowserCreatorWelcomeBackTest,
 }
 #endif  // defined(OS_WIN)
 
-#if defined(OS_LINUX)
-#define MAYBE_WelcomeBackStandardNoPolicy DISABLED_WelcomeBackStandardNoPolicy
-#else
-#define MAYBE_WelcomeBackStandardNoPolicy WelcomeBackStandardNoPolicy
-#endif
 IN_PROC_BROWSER_TEST_F(StartupBrowserCreatorWelcomeBackTest,
-                       MAYBE_WelcomeBackStandardNoPolicy) {
+                       WelcomeBackStandardNoPolicy) {
   ASSERT_NO_FATAL_FAILURE(
       StartBrowser(StartupBrowserCreator::WelcomeBackPage::kWelcomeStandard,
                    PolicyVariant()));