Issue #4873: Use manifest placeholder to inject sharedUserId.

app/build.gradle

@@ -72,6 +72,14 @@ android {
         fennecProduction releaseTemplate >> {
             buildConfigField "boolean", "USE_RELEASE_VERSIONING", "true"
             applicationIdSuffix ".firefox"
+            manifestPlaceholders = [
+                // This release type is meant to replace Firefox (Release channel) and therefore needs to inherit
+                // its sharedUserId for all eternity. Shipping an app update without sharedUserId can have
+                // fatal consequences. For example see:
+                //  - https://issuetracker.google.com/issues/36924841
+                //  - https://issuetracker.google.com/issues/36905922
+                "sharedUserId": "org.mozilla.firefox.sharedID"
+            ]
         }
     }
 

app/src/fennecProduction/AndroidManifest.xml

@@ -7,6 +7,6 @@
                 - https://issuetracker.google.com/issues/36905922
 -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-      android:sharedUserId="org.mozilla.firefox.sharedID">
+      android:sharedUserId="${sharedUserId}">
 </manifest>