[fenix] For https://github.com/mozilla-mobile/fenix/issues/1836 - Update theme based on if session private (https://github.com/mozilla-mobile/fenix/pull/2099)

app/src/main/java/org/mozilla/fenix/HomeActivity.kt

@@ -218,6 +218,14 @@ open class HomeActivity : AppCompatActivity() {
         }
     }
 
+    fun updateThemeForSession(session: Session) {
+        if (session.private && !themeManager.currentTheme.isPrivate()) {
+            browsingModeManager.mode = BrowsingModeManager.Mode.Private
+        } else if (!session.private && themeManager.currentTheme.isPrivate()) {
+            browsingModeManager.mode = BrowsingModeManager.Mode.Normal
+        }
+    }
+
     private fun subscribeToSessions(): SessionManager.Observer {
 
         return object : SessionManager.Observer {
@@ -244,6 +252,11 @@ open class HomeActivity : AppCompatActivity() {
                     it.register(singleSessionObserver)
                 }
             }
+
+            override fun onSessionSelected(session: Session) {
+                super.onSessionSelected(session)
+                updateThemeForSession(session)
+            }
         }.also { components.core.sessionManager.register(it) }
     }
 

app/src/main/java/org/mozilla/fenix/browser/BrowserFragment.kt

@@ -302,6 +302,9 @@ class BrowserFragment : Fragment(), BackHandler, CoroutineScope,
 
     override fun onResume() {
         super.onResume()
+        getSessionById()?.let {
+            (activity as HomeActivity).updateThemeForSession(it)
+        }
         context?.components?.core?.let {
             val preferredColorScheme = it.getPreferredColorScheme()
             if (it.engine.settings.preferredColorScheme != preferredColorScheme) {