[StartSurface] Disable start surface for low end device

This CL also fixes the new tab button is missing on start
tab switcher surface.

Screenshots:
https://drive.google.com/a/google.com/file/d/1R4_oyeIz6_VuwMellLzPI7zQ2ef04AWX/view?usp=sharing
https://drive.google.com/a/google.com/file/d/1R0ASrrY8v50Z9E2bbGI-al_kKrjlI16p/view?usp=sharing

Bug: 1042006
Change-Id: Ie9663daf6cc0cb32c63975d65adfce9bb990ef4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003289Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732482}

chrome/android/java/src/org/chromium/chrome/browser/flags/FeatureUtilities.java

@@ -412,7 +412,8 @@ public class FeatureUtilities {
      * @return Whether the Start Surface is enabled.
      */
     public static boolean isStartSurfaceEnabled() {
-        return isFlagEnabled(ChromePreferenceKeys.FLAGS_CACHED_START_SURFACE_ENABLED, false);
+        return isFlagEnabled(ChromePreferenceKeys.FLAGS_CACHED_START_SURFACE_ENABLED, false)
+                && !SysUtils.isLowEndDevice();
     }
 
     private static void cachePaintPreviewTestEnabled() {

chrome/android/java/src/org/chromium/chrome/browser/tasks/ReturnToChromeExperimentsUtil.java

@@ -21,6 +21,7 @@ import org.chromium.chrome.browser.ntp.NewTabPage;
 import org.chromium.chrome.browser.partnercustomizations.HomepageManager;
 import org.chromium.chrome.browser.tab.TabLaunchType;
 import org.chromium.chrome.browser.tabmodel.TabModel;
+import org.chromium.chrome.browser.util.AccessibilityUtil;
 import org.chromium.content_public.browser.LoadUrlParams;
 import org.chromium.ui.base.PageTransition;
 
@@ -180,10 +181,11 @@ public final class ReturnToChromeExperimentsUtil {
      * @return Whether Start Surface should be shown as the home page, otherwise false.
      */
     public static boolean shouldShowStartSurfaceAsTheHomePage() {
-        // Note that we should only show StartSurface as the HomePage if Single Pane is enabled and
-        // HomePage is not customized.
+        // Note that we should only show StartSurface as the HomePage if Single Pane is enabled,
+        // HomePage is not customized and accessibility is not enabled.
         String homePageUrl = HomepageManager.getHomepageUri();
         return FeatureUtilities.isStartSurfaceSinglePaneEnabled()
-                && (TextUtils.isEmpty(homePageUrl) || NewTabPage.isNTPUrl(homePageUrl));
+                && (TextUtils.isEmpty(homePageUrl) || NewTabPage.isNTPUrl(homePageUrl))
+                && !AccessibilityUtil.isAccessibilityEnabled();
     }
 }

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/StartSurfaceToolbarMediator.java

@@ -28,6 +28,7 @@ import org.chromium.chrome.browser.tabmodel.TabModelSelector;
 import org.chromium.chrome.browser.tabmodel.TabModelSelectorObserver;
 import org.chromium.chrome.browser.toolbar.IncognitoStateProvider;
 import org.chromium.chrome.browser.ui.appmenu.AppMenuButtonHelper;
+import org.chromium.chrome.browser.util.AccessibilityUtil;
 import org.chromium.components.search_engines.TemplateUrlService.TemplateUrlServiceObserver;
 import org.chromium.ui.modelutil.PropertyModel;
 
@@ -55,15 +56,13 @@ class StartSurfaceToolbarMediator {
         mTemplateUrlObserver = new TemplateUrlServiceObserver() {
             @Override
             public void onTemplateURLServiceChanged() {
-                updateLogoVisibility(mOverviewModeState,
-                        TemplateUrlServiceFactory.get().isDefaultSearchEngineGoogle());
+                updateLogoVisibility(TemplateUrlServiceFactory.get().isDefaultSearchEngineGoogle());
             }
         };
 
         TemplateUrlServiceFactory.get().addObserver(mTemplateUrlObserver);
         mIsGoogleSearchEngine = TemplateUrlServiceFactory.get().isDefaultSearchEngineGoogle();
-        updateLogoVisibility(
-                mOverviewModeState, TemplateUrlServiceFactory.get().isDefaultSearchEngineGoogle());
+        updateLogoVisibility(TemplateUrlServiceFactory.get().isDefaultSearchEngineGoogle());
     }
 
     void destroy() {
@@ -115,6 +114,7 @@ class StartSurfaceToolbarMediator {
 
     void onAccessibilityStatusChanged(boolean enabled) {
         mPropertyModel.set(ACCESSIBILITY_ENABLED, enabled);
+        updateNewTabButtonVisibility();
     }
 
     void onBottomToolbarVisibilityChanged(boolean isVisible) {}
@@ -128,10 +128,9 @@ class StartSurfaceToolbarMediator {
                 @Override
                 public void onOverviewModeStateChanged(
                         @OverviewModeState int overviewModeState, boolean showTabSwitcherToolbar) {
-                    boolean isShownTabswitcherState =
-                            overviewModeState == OverviewModeState.SHOWN_TABSWITCHER;
-                    mPropertyModel.set(NEW_TAB_BUTTON_IS_VISIBLE, isShownTabswitcherState);
-                    updateLogoVisibility(overviewModeState, mIsGoogleSearchEngine);
+                    mOverviewModeState = overviewModeState;
+                    updateNewTabButtonVisibility();
+                    updateLogoVisibility(mIsGoogleSearchEngine);
                 }
                 @Override
                 public void onOverviewModeFinishedShowing() {
@@ -148,9 +147,7 @@ class StartSurfaceToolbarMediator {
         mOverviewModeBehavior.addOverviewModeObserver(mOverviewModeObserver);
     }
 
-    private void updateLogoVisibility(
-            @OverviewModeState int overviewModeState, boolean isGoogleSearchEngine) {
-        mOverviewModeState = overviewModeState;
+    private void updateLogoVisibility(boolean isGoogleSearchEngine) {
         mIsGoogleSearchEngine = isGoogleSearchEngine;
         boolean shouldShowLogo =
                 (mOverviewModeState == OverviewModeState.SHOWN_HOMEPAGE
@@ -158,4 +155,13 @@ class StartSurfaceToolbarMediator {
                 && mIsGoogleSearchEngine;
         mPropertyModel.set(LOGO_IS_VISIBLE, shouldShowLogo);
     }
+
+    private void updateNewTabButtonVisibility() {
+        // This toolbar is only shown for tab switcher when accessibility is enabled. Note that
+        // OverviewListLayout will be shown as the tab switcher instead of the star surface.
+        boolean isShownTabswitcherState = mOverviewModeState == OverviewModeState.SHOWN_TABSWITCHER
+                || mOverviewModeState == OverviewModeState.SHOWN_TABSWITCHER_TASKS_ONLY
+                || AccessibilityUtil.isAccessibilityEnabled();
+        mPropertyModel.set(NEW_TAB_BUTTON_IS_VISIBLE, isShownTabswitcherState);
+    }
 }