weblayer: fix possible crash in destruction

getHandler() may return null, which the code was not
prepared for.

I'll work out a test case separately.

BUG=1075662
TEST=none

Change-Id: Ie880cba5a7bcfeaf848a71d667c36cc30e5b57ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2169021Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763323}

weblayer/browser/java/org/chromium/weblayer_private/TopControlsContainerView.java

@@ -134,7 +134,7 @@ class TopControlsContainerView extends FrameLayout {
         TopControlsContainerViewJni.get().deleteTopControlsContainerView(
                 mNativeTopControlsContainerView, TopControlsContainerView.this);
         if (mSystemUiFullscreenResizeRunnable != null) {
-            getHandler().removeCallbacks(mSystemUiFullscreenResizeRunnable);
+            removeCallbacks(mSystemUiFullscreenResizeRunnable);
             mSystemUiFullscreenResizeRunnable = null;
         }
     }
@@ -312,7 +312,7 @@ class TopControlsContainerView extends FrameLayout {
     private void didToggleFullscreenModeForTab(final boolean isFullscreen) {
         // Delay hiding until after the animation. This comes from Chrome code.
         if (mSystemUiFullscreenResizeRunnable != null) {
-            getHandler().removeCallbacks(mSystemUiFullscreenResizeRunnable);
+            removeCallbacks(mSystemUiFullscreenResizeRunnable);
         }
         mSystemUiFullscreenResizeRunnable = () -> processFullscreenChanged(isFullscreen);
         long delay = isFullscreen ? SYSTEM_UI_VIEWPORT_UPDATE_DELAY_MS : 0;