Add internal product flavor.

app/build.gradle

@@ -246,6 +246,13 @@ android {
             buildConfigField "boolean", "PLAY_STORE_DISABLED", "true"
             buildConfigField "String", "NOPLAY_UPDATE_URL", "\"$ext.websiteUpdateUrl\""
         }
+
+        internal {
+            dimension "none"
+            ext.websiteUpdateUrl = "null"
+            buildConfigField "boolean", "PLAY_STORE_DISABLED", "false"
+            buildConfigField "String", "NOPLAY_UPDATE_URL", "$ext.websiteUpdateUrl"
+        }
     }
 
     android.applicationVariants.all { variant ->

app/src/internal/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/core_red_shade"/>
+    <foreground android:drawable="@drawable/ic_launcher_foreground"/>
+</adaptive-icon>

app/src/internal/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<resources>
+  <string name="app_name">Signal (Internal)</string>
+</resources>