Android Project: Opt into splash behavior by default. (#49096)

packages/flutter_tools/templates/app/android.tmpl/app/src/main/AndroidManifest.xml.tmpl

@@ -25,6 +25,25 @@
                 android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
                 android:value="true" />
             {{/useAndroidEmbeddingV2}}
+            {{#useAndroidEmbeddingV2}}
+            <!-- Specifies an Android theme to apply to this Activity as soon as
+                 the Android process has started. This theme is visible to the user
+                 while the Flutter UI initializes. After that, this theme continues
+                 to determine the Window background behind the Flutter UI. -->
+            <meta-data
+              android:name="io.flutter.embedding.android.NormalTheme"
+              android:resource="@style/NormalTheme"
+              />
+            <!-- Displays an Android View that continues showing the launch screen
+                 Drawable until Flutter paints its first frame, then this splash
+                 screen fades out. A splash screen is useful to avoid any visual
+                 gap between the end of Android's launch screen and the painting of
+                 Flutter's first frame. -->
+            <meta-data
+              android:name="io.flutter.embedding.android.SplashScreenDrawable"
+              android:resource="@drawable/launch_background"
+              />
+            {{/useAndroidEmbeddingV2}}
             <intent-filter>
                 <action android:name="android.intent.action.MAIN"/>
                 <category android:name="android.intent.category.LAUNCHER"/>

packages/flutter_tools/templates/app/android.tmpl/app/src/main/res/values/styles.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
+    <!-- Theme applied to the Android Window while the process is starting -->
     <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
         <!-- Show a splash screen on the activity. Automatically removed when
              Flutter draws its first frame -->
         <item name="android:windowBackground">@drawable/launch_background</item>
     </style>
+    <!-- Theme applied to the Android Window as soon as the process has started.
+         This theme determines the color of the Android Window while your
+         Flutter UI initializes, as well as behind your Flutter UI while its
+         running.
+         
+         This Theme is only used starting with V2 of Flutter's Android embedding. -->
+    <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <item name="android:windowBackground">@android:color/white</item>
+    </style>
 </resources>