[StartSurface] Destroy incognito switch coordinator if needed

Bug: 1025296
Change-Id: Ic72b26024d7125587b3803d1d3bb7655cc0f7efe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2013638
Auto-Submit: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734258}

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

@@ -43,6 +43,7 @@ class StartSurfaceToolbarCoordinator {
      */
     void destroy() {
         mToolbarMediator.destroy();
+        if (mIncognitoSwitchCoordinator != null) mIncognitoSwitchCoordinator.destroy();
     }
     /**
      * @param appMenuButtonHelper The helper for managing menu button interactions.