[Start] Incognito tab switcher should be shown on resume.

When tab switcher return "immediate" is enabled, we shouldn't show the
Incognito Start surface (single) when resuming Chrome. Instead, we will
show the Incognito tab switcher.

Bug: 1153713
Change-Id: I2710e1bad9bca3f577354367e2b1363e72561812
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2565730
Commit-Queue: Xi Han <hanxi@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832109}

chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/StartSurfaceMediator.java

@@ -930,6 +930,9 @@ class StartSurfaceMediator
                         ? StartSurfaceState.SHOWN_HOMEPAGE
                         : mPreviousStartSurfaceState;
             } else if (mStartSurfaceState == StartSurfaceState.SHOWING_START) {
+                if (mTabModelSelector.isIncognitoSelected() && !mShowStackTabSwitcher) {
+                    return StartSurfaceState.SHOWN_TABSWITCHER;
+                }
                 return StartSurfaceState.SHOWN_HOMEPAGE;
             } else if (mStartSurfaceState == StartSurfaceState.SHOWING_TABSWITCHER) {
                 return StartSurfaceState.SHOWN_TABSWITCHER;

chrome/android/features/start_surface/internal/javatests/src/org/chromium/chrome/features/start_surface/StartSurfaceTest.java

@@ -808,12 +808,14 @@ public class StartSurfaceTest {
     @Test
     @MediumTest
     @Feature({"StartSurface"})
+    // clang-format off
     @CommandLineFlags.Add({BASE_PARAMS + "/single/exclude_mv_tiles/true"
             + "/show_last_active_tab_only/true/show_stack_tab_switcher/true"})
-    public void
-    testShow_SingleAsHomepageV2_FromResumeShowStart() throws Exception {
+    public void testShow_SingleAsHomepageV2_FromResumeShowStart() throws Exception {
         // clang-format on
-        if (!mImmediateReturn) return;
+        if (!mImmediateReturn) {
+            onView(withId(org.chromium.chrome.tab_ui.R.id.home_button)).perform(click());
+        }
 
         ChromeTabbedActivity cta = mActivityTestRule.getActivity();
         CriteriaHelper.pollUiThread(
@@ -833,11 +835,60 @@ public class StartSurfaceTest {
         // Simulates pressing Chrome's icon and launching Chrome from warm start.
         mActivityTestRule.resumeMainActivityFromLauncher();
 
+        waitForTabModel();
+        if (mImmediateReturn) {
+            CriteriaHelper.pollUiThread(()
+                                                -> cta.getLayoutManager() != null
+                            && cta.getLayoutManager().overviewVisible());
+            // Verifies that with the vertical tab switcher, the regular Start surface is shown when
+            // resuming.
+            assertFalse(cta.getTabModelSelector().getCurrentModel().isIncognito());
+            assertThat(cta.getTabModelSelector().getCurrentModel().getCount(), equalTo(0));
+        } else {
+            assertTrue(cta.getTabModelSelector().getCurrentModel().isIncognito());
+            onViewWaiting(allOf(withId(R.id.new_tab_incognito_container), isDisplayed()));
+        }
+    }
+
+    @Test
+    @MediumTest
+    @Feature({"StartSurface"})
+    // clang-format off
+    @CommandLineFlags.Add({BASE_PARAMS + "/single"})
+    public void testShow_SingleAsHomepage_FromResumeShowStart() throws Exception {
+        // clang-format on
+        if (!mImmediateReturn) {
+            onView(withId(org.chromium.chrome.tab_ui.R.id.home_button)).perform(click());
+        }
+
+        ChromeTabbedActivity cta = mActivityTestRule.getActivity();
         CriteriaHelper.pollUiThread(
                 () -> cta.getLayoutManager() != null && cta.getLayoutManager().overviewVisible());
         waitForTabModel();
-        assertFalse(cta.getTabModelSelector().getCurrentModel().isIncognito());
-        assertThat(cta.getTabModelSelector().getCurrentModel().getCount(), equalTo(0));
+        TestThreadUtils.runOnUiThreadBlocking(
+                () -> { cta.getTabModelSelector().getModel(false).closeAllTabs(); });
+        TabUiTestHelper.verifyTabModelTabCount(cta, 0, 0);
+        assertTrue(cta.getLayoutManager().overviewVisible());
+        TestThreadUtils.runOnUiThreadBlocking(
+                () -> cta.getTabCreator(true /*incognito*/).launchNTP());
+        TabUiTestHelper.verifyTabModelTabCount(cta, 0, 1);
+
+        // Simulates pressing the Android's home button and bringing Chrome to the background.
+        pressHome();
+
+        // Simulates pressing Chrome's icon and launching Chrome from warm start.
+        mActivityTestRule.resumeMainActivityFromLauncher();
+
+        waitForTabModel();
+        assertTrue(cta.getTabModelSelector().getCurrentModel().isIncognito());
+        if (mImmediateReturn) {
+            CriteriaHelper.pollUiThread(()
+                                                -> cta.getLayoutManager() != null
+                            && cta.getLayoutManager().overviewVisible());
+            onViewWaiting(allOf(withId(R.id.secondary_tasks_surface_view), isDisplayed()));
+        } else {
+            onViewWaiting(allOf(withId(R.id.new_tab_incognito_container), isDisplayed()));
+        }
     }
 
     @Test