[StartSurface] Fix setTabSwitcherToolbarVisibility crash

Bug: 1021399
Change-Id: I7b9aa63e6613b495614b38acbf850786c159054b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1899408
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712678}

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

@@ -415,7 +415,10 @@ class StartSurfaceMediator
             mSecondaryTasksSurfacePropertyModel.set(IS_INCOGNITO, mIsIncognito);
         }
 
-        notifyStateChange();
+        // TODO(crbug.com/1021399): This looks not needed since there is no way to change incognito
+        // mode when focusing on the omnibox and incognito mode change won't affect the visibility
+        // of the tab switcher toolbar.
+        if (mPropertyModel.get(IS_SHOWING_OVERVIEW)) notifyStateChange();
     }
 
     private void setSecondaryTasksSurfaceVisibility(boolean isVisible) {
@@ -436,6 +439,7 @@ class StartSurfaceMediator
 
     private void notifyStateChange() {
         assert mSurfaceMode != SurfaceMode.NO_START_SURFACE;
+        assert mPropertyModel.get(IS_SHOWING_OVERVIEW);
 
         if (mStateObserver != null) {
             mStateObserver.onStateChanged(shouldShowTabSwitcherToolbar());

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

@@ -163,7 +163,8 @@ class TabSwitcherModeTTCoordinatorPhone implements TemplateUrlServiceObserver {
     }
 
     void setTabSwitcherToolbarVisibility(boolean shouldShowTabSwitcherToolbar) {
-        if ((mTabSwitcherModeToolbar.getVisibility() == View.VISIBLE)
+        if (mTabSwitcherModeToolbar == null
+                || (mTabSwitcherModeToolbar.getVisibility() == View.VISIBLE)
                         == shouldShowTabSwitcherToolbar) {
             return;
         }