[platform_channels] adds iOS implementation for platform image demo (#575)

platform_channels/ios/Runner/AppDelegate.swift

@@ -26,6 +26,19 @@ import Flutter
             }
         })
         
+        FlutterBasicMessageChannel(name: "platformImageDemo", binaryMessenger: flutterViewController.binaryMessenger, codec: FlutterStandardMessageCodec.sharedInstance()).setMessageHandler{
+            (message: Any?, reply: FlutterReply) -> Void in
+            
+            if(message as! String == "getImage") {
+                guard let image = UIImage(named: "eat_new_orleans.jpg") else {
+                    reply(nil)
+                    return
+                }
+                
+                reply(FlutterStandardTypedData(bytes: image.jpegData(compressionQuality: 1)!))
+            }
+        }
+        
         GeneratedPluginRegistrant.register(with: self)
         return super.application(application, didFinishLaunchingWithOptions: launchOptions)
     }

platform_channels/ios/Runner/Assets.xcassets/Contents.json

@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

platform_channels/ios/Runner/Assets.xcassets/eat_new_orleans.imageset/Contents.json

@@ -0,0 +1,21 @@
+{
+  "images" : [
+    {
+      "filename" : "eat_new_orleans.jpg",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}