Create template splash screens for Android and iOS (#11505)

* Add iOS template

* Android

* Let the engine reset the theme without the activity knowing

* Small tweak

* Replace assets with different vectors

* Let the template hookup have no actual image assets

* Add back placeholder assets with 1px transparent pngs

* Fix drawable xml

* clean up an extraneous line in the storyboard xml

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

@@ -12,10 +12,14 @@
          In most cases you can leave this as-is, but you if you want to provide
          additional functionality it is fine to subclass or reimplement
          FlutterApplication and put your custom class here. -->
-    <application android:name="io.flutter.app.FlutterApplication" android:label="{{projectName}}" android:icon="@mipmap/ic_launcher">
-        <activity android:name=".MainActivity"
+    <application
+        android:name="io.flutter.app.FlutterApplication"
+        android:label="{{projectName}}"
+        android:icon="@mipmap/ic_launcher">
+        <activity
+            android:name=".MainActivity"
             android:launchMode="singleTop"
-                  android:theme="@android:style/Theme.Black.NoTitleBar"
+            android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection"
             android:hardwareAccelerated="true"
             android:windowSoftInputMode="adjustResize">

packages/flutter_tools/templates/create/android.tmpl/app/src/main/res/drawable/launch_background.xml

+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@android:color/white" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>

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

+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <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>
+</resources>

packages/flutter_tools/templates/create/ios.tmpl/Runner/Assets.xcassets/LaunchImage.imageset/Contents.json

+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "filename" : "LaunchImage.png",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "LaunchImage@2x.png",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "LaunchImage@3x.png",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}

packages/flutter_tools/templates/create/ios.tmpl/Runner/Assets.xcassets/LaunchImage.imageset/README.md

+# Launch Screen Assets
+
+You can customize the launch screen with your own desired assets by replacing the image files in this directory.
+
+You can also do it by opening your Flutter project's Xcode project with `open ios/Runner.xcworkspace`, selecting `Runner/Assets.xcassets` in the Project Navigator and dropping in the desired images.
\ No newline at end of file

packages/flutter_tools/templates/create/ios.tmpl/Runner/Base.lproj/LaunchScreen.storyboard

 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="10117" systemVersion="15F34" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" launchScreen="YES" useTraitCollections="YES" initialViewController="01J-lp-oVM">
+<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="12121" systemVersion="16G29" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" launchScreen="YES" colorMatched="YES" initialViewController="01J-lp-oVM">
     <dependencies>
         <deployment identifier="iOS"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="10085"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="12089"/>
     </dependencies>
     <scenes>
         <!--View Controller-->
@@ -10,13 +10,20 @@
             <objects>
                 <viewController id="01J-lp-oVM" sceneMemberID="viewController">
                     <layoutGuides>
-                        <viewControllerLayoutGuide type="top" id="Llm-lL-Icb"/>
-                        <viewControllerLayoutGuide type="bottom" id="xb3-aO-Qok"/>
+                        <viewControllerLayoutGuide type="top" id="Ydg-fD-yQy"/>
+                        <viewControllerLayoutGuide type="bottom" id="xbc-2k-c8Z"/>
                     </layoutGuides>
                     <view key="view" contentMode="scaleToFill" id="Ze5-6b-2t3">
-                        <rect key="frame" x="0.0" y="0.0" width="600" height="600"/>
                         <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
-                        <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>
+                        <subviews>
+                            <imageView opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center" image="LaunchImage" translatesAutoresizingMaskIntoConstraints="NO" id="YRO-k0-Ey4">
+                            </imageView>
+                        </subviews>
+                        <color key="backgroundColor" red="1" green="1" blue="1" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
+                        <constraints>
+                            <constraint firstItem="YRO-k0-Ey4" firstAttribute="centerX" secondItem="Ze5-6b-2t3" secondAttribute="centerX" id="1a2-6s-vTC"/>
+                            <constraint firstItem="YRO-k0-Ey4" firstAttribute="centerY" secondItem="Ze5-6b-2t3" secondAttribute="centerY" id="4X2-HB-R7a"/>
+                        </constraints>
                     </view>
                 </viewController>
                 <placeholder placeholderIdentifier="IBFirstResponder" id="iYj-Kq-Ea1" userLabel="First Responder" sceneMemberID="firstResponder"/>
@@ -24,4 +31,7 @@
             <point key="canvasLocation" x="53" y="375"/>
         </scene>
     </scenes>
+    <resources>
+        <image name="LaunchImage" width="168" height="185"/>
+    </resources>
 </document>