chrome/android/java/res/drawable/action_bar_activity_bg.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2015 The Chromium Authors. All rights reserved.
     Use of this source code is governed by a BSD-style license that can be
     found in the LICENSE file. -->

<!-- On pre-KitKat devices the window background extends above the action bar
     and is normally hidden behind the status bar, but during window
     transitions, is visible and looks glitchy. As a workaround, we make the top
     50dp of the window background transparent. 50dp is greater than the status
     bar height (to prevent the visual glitch) and less than the status bar +
     action bar height (to ensure the background covers the entire activity). On
     KitKat and later devices, Android clips the window background correctly and
     these shenanigans aren't needed. http://crbug.com/448012 -->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:drawable="@color/modern_primary_color"
        android:top="50dp" />
</layer-list>