Finish StartSurfaceToolbar animation correctly.

Bug: 1143164
Change-Id: Iada70f9d6651de1f0bb2797a65880ec3b4fe41b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2511718Reviewed-by: Xi Han <hanxi@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Commit-Queue: Hao Dong <spdonghao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823847}

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

@@ -260,7 +260,7 @@ class StartSurfaceToolbarView extends RelativeLayout {
 
         if (mVisibilityAnimator != null) {
             mVisibilityAnimator.cancel();
-            mVisibilityAnimator = null;
+            finishAnimation(showStartSurfaceToolbar);
         }
 
         mIsShowing = showStartSurfaceToolbar;