add compose icon.

app/src/main/res/drawable/ic_compose_white_24dp.xml

+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0">
+    <path
+        android:fillColor="#FFFFFFFF"
+        android:pathData="M3,17.25V21h3.75L17.81,9.94l-3.75,-3.75L3,17.25zM20.71,7.04c0.39,-0.39 0.39,-1.02 0,-1.41l-2.34,-2.34c-0.39,-0.39 -1.02,-0.39 -1.41,0l-1.83,1.83 3.75,3.75 1.83,-1.83z"/>
+</vector>

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

 <?xml version="1.0" encoding="utf-8"?>
 <FrameLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     >
@@ -25,5 +26,6 @@
       android:layout_height="wrap_content"
       android:layout_gravity="end|bottom"
       android:layout_margin="@dimen/margin_16"
+      app:srcCompat="@drawable/ic_compose_white_24dp"
       />
 </FrameLayout>
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