Use floating action button in the cast demo app

PiperOrigin-RevId: 233723028

demos/cast/build.gradle

@@ -56,6 +56,7 @@ dependencies {
     implementation project(modulePrefix + 'library-smoothstreaming')
     implementation project(modulePrefix + 'library-ui')
     implementation project(modulePrefix + 'extension-cast')
+    implementation 'com.android.support:design:' + supportLibraryVersion
     implementation 'com.android.support:support-v4:' + supportLibraryVersion
     implementation 'com.android.support:appcompat-v7:' + supportLibraryVersion
     implementation 'com.android.support:recyclerview-v7:' + supportLibraryVersion

demos/cast/src/main/res/drawable/ic_add_circle_white_24dp.xml → demos/cast/src/main/res/drawable/ic_plus.xml

@@ -13,8 +13,12 @@
      See the License for the specific language governing permissions and
      limitations under the License.
 -->
-<vector android:alpha="0.8" android:height="24dp" android:viewportHeight="24.0"
-    android:viewportWidth="24.0" android:width="24dp"
-    xmlns:android="http://schemas.android.com/apk/res/android">
-  <path android:fillColor="#FFFFFF" android:pathData="M12,2C6.48,2 2,6.48 2,12s4.48,10 10,10 10,-4.48 10,-10S17.52,2 12,2zM17,13h-4v4h-2v-4L7,13v-2h4L11,7h2v4h4v2z"/>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:height="24.0dp"
+    android:viewportHeight="24.0"
+    android:viewportWidth="24.0"
+    android:width="24.0dp" >
+  <path
+      android:fillColor="#FFFFFFFF"
+      android:pathData="M18,13h-5v5c0,0.55 -0.45,1 -1,1h0c-0.55,0 -1,-0.45 -1,-1v-5H6c-0.55,0 -1,-0.45 -1,-1v0c0,-0.55 0.45,-1 1,-1h5V6c0,-0.55 0.45,-1 1,-1h0c0.55,0 1,0.45 1,1v5h5c0.55,0 1,0.45 1,1v0C19,12.55 18.55,13 18,13z"/>
 </vector>

demos/cast/src/main/res/layout/main_activity.xml

@@ -38,14 +38,14 @@
         android:scrollbars="vertical"
         android:fadeScrollbars="false"/>
 
-    <ImageButton android:id="@+id/add_sample_button"
-        android:background="@drawable/ic_add_circle_white_24dp"
+    <android.support.design.widget.FloatingActionButton android:id="@+id/add_sample_button"
+        android:src="@drawable/ic_plus"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_alignParentEnd="true"
         android:layout_alignParentRight="true"
         android:layout_alignParentBottom="true"
-        android:padding="30dp"
+        android:layout_margin="16dp"
         android:contentDescription="@string/add_samples"/>
 
   </RelativeLayout>