[iOS][DarkMode] Update launch images

Replace brand image and logo with versions containing alpha.
Remove unused 1x image.
Add dark mode to brand image.
This requires to be compiled with Xcode 11 (iOS SDK 13).

Bug: 976640
Change-Id: Id19d571d8e6fd85ad616329616c0eb3319867164
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1713538Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688530}

ios/chrome/app/resources/BUILD.gn

@@ -98,7 +98,6 @@ appiconset("chromium_icons") {
 imageset("launchscreen_app_logo") {
   sources = [
     "launchscreen_app_logo.imageset/Contents.json",
-    "launchscreen_app_logo.imageset/launchscreen_app_logo.png",
     "launchscreen_app_logo.imageset/launchscreen_app_logo@2x.png",
     "launchscreen_app_logo.imageset/launchscreen_app_logo@3x.png",
   ]
@@ -107,9 +106,10 @@ imageset("launchscreen_app_logo") {
 imageset("launchscreen_brand_name") {
   sources = [
     "launchscreen_brand_name.imageset/Contents.json",
-    "launchscreen_brand_name.imageset/launchscreen_brand_name.png",
-    "launchscreen_brand_name.imageset/launchscreen_brand_name@2x.png",
-    "launchscreen_brand_name.imageset/launchscreen_brand_name@3x.png",
+    "launchscreen_brand_name.imageset/launchscreen_brand_name_dark@2x.png",
+    "launchscreen_brand_name.imageset/launchscreen_brand_name_dark@3x.png",
+    "launchscreen_brand_name.imageset/launchscreen_brand_name_light@2x.png",
+    "launchscreen_brand_name.imageset/launchscreen_brand_name_light@3x.png",
   ]
 }
 

ios/chrome/app/resources/launchscreen_app_logo.imageset/Contents.json

 {
   "images" : [
-    {
-      "idiom" : "universal",
-      "filename" : "launchscreen_app_logo.png",
-      "scale" : "1x"
-    },
     {
       "idiom" : "universal",
       "filename" : "launchscreen_app_logo@2x.png",

ios/chrome/app/resources/launchscreen_brand_name.imageset/Contents.json

@@ -2,17 +2,48 @@
   "images" : [
     {
       "idiom" : "universal",
-      "filename" : "launchscreen_brand_name.png",
       "scale" : "1x"
     },
     {
       "idiom" : "universal",
-      "filename" : "launchscreen_brand_name@2x.png",
+      "scale" : "1x",
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ]
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "launchscreen_brand_name_light@2x.png",
       "scale" : "2x"
     },
     {
       "idiom" : "universal",
-      "filename" : "launchscreen_brand_name@3x.png",
+      "filename" : "launchscreen_brand_name_dark@2x.png",
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "launchscreen_brand_name_light@3x.png",
+      "scale" : "3x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "launchscreen_brand_name_dark@3x.png",
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
       "scale" : "3x"
     }
   ],