Replace CoordinatorLayout to RelativeLayout

app/src/main/res/layout/activity_chat_room.xml

 <?xml version="1.0" encoding="utf-8"?>
-<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:theme="@style/AppTheme">
 
-    <include layout="@layout/app_bar" />
+    <include
+        android:id="@+id/layout_app_bar"
+        layout="@layout/app_bar" />
 
     <FrameLayout
         android:id="@+id/fragment_container"
         android:layout_width="match_parent"
-        android:layout_height="match_parent" />
+        android:layout_height="match_parent"
+        android:layout_below="@+id/layout_app_bar" />
 
-</android.support.design.widget.CoordinatorLayout>
\ No newline at end of file
+</RelativeLayout>
\ No newline at end of file