File access permission for gallery_saver.

iOS
Add the following keys to your Info.plist file, located in <project root>/ios/Runner/Info.plist:
NSPhotoLibraryUsageDescription - describe why your app needs permission for the photo library. This is called Privacy - Photo Library Usage Description in the visual editor.

Android
android.permission.WRITE_EXTERNAL_STORAGE - Permission for usage of external storage

example/android/app/src/debug/AndroidManifest.xml

@@ -4,4 +4,5 @@
          to allow setting breakpoints, to provide hot reload, etc.
     -->
     <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
 </manifest>

example/android/app/src/main/AndroidManifest.xml

@@ -1,5 +1,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.example.app">
+    <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <application
         android:name="${applicationName}"
         android:label="app"

example/android/app/src/profile/AndroidManifest.xml

@@ -4,4 +4,5 @@
          to allow setting breakpoints, to provide hot reload, etc.
     -->
     <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
 </manifest>

example/ios/Runner/Info.plist

@@ -20,6 +20,8 @@
 	<string>????</string>
 	<key>CFBundleVersion</key>
 	<string>$(FLUTTER_BUILD_NUMBER)</string>
+    <key>NSPhotoLibraryUsageDescription</key>
+    <string>Need to save image</string>
 	<key>LSRequiresIPhoneOS</key>
 	<true/>
 	<key>UILaunchStoryboardName</key>