[fenix] Closes https://github.com/mozilla-mobile/fenix/issues/3091 - Hide Pull to Refresh under flag (https://github.com/mozilla-mobile/fenix/pull/3092)

This was merged in after feature freeze so we're pulling it out for
now. Pull to refresh will continue to work in debug mode so that the
design can be iterated on easily.

app/build.gradle

@@ -250,6 +250,7 @@ android.applicationVariants.all { variant ->
 // Feature build flags
 // -------------------------------------------------------------------------------------------------
     buildConfigField 'Boolean', 'SEND_TAB_ENABLED', (buildType == "nightly" || isDebug).toString()
+    buildConfigField 'Boolean', 'PULL_TO_REFRESH_ENABLED', (false).toString()
 }
 
 androidExtensions {

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

@@ -56,6 +56,7 @@ import mozilla.components.support.ktx.android.view.enterToImmersiveMode
 import mozilla.components.support.ktx.android.view.exitImmersiveModeIfNeeded
 import mozilla.components.support.ktx.kotlin.toUri
 import org.mozilla.fenix.BrowsingModeManager
+import org.mozilla.fenix.BuildConfig
 import org.mozilla.fenix.FenixViewModelProvider
 import org.mozilla.fenix.HomeActivity
 import org.mozilla.fenix.IntentReceiverActivity
@@ -185,7 +186,7 @@ class BrowserFragment : Fragment(), BackHandler, CoroutineScope {
         return view
     }
 
-    @Suppress("LongMethod")
+    @Suppress("LongMethod", "ComplexMethod")
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
 
@@ -334,18 +335,23 @@ class BrowserFragment : Fragment(), BackHandler, CoroutineScope {
             view = view
         )
 
-        val primaryTextColor = ThemeManager.resolveAttribute(R.attr.primaryText, requireContext())
-        view.swipeRefresh.setColorSchemeColors(primaryTextColor)
-        swipeRefreshFeature.set(
-            feature = SwipeRefreshFeature(
-                requireComponents.core.sessionManager,
-                requireComponents.useCases.sessionUseCases.reload,
-                view.swipeRefresh,
-                customTabSessionId
-            ),
-            owner = this,
-            view = view
-        )
+        if (BuildConfig.PULL_TO_REFRESH_ENABLED) {
+            val primaryTextColor = ThemeManager.resolveAttribute(R.attr.primaryText, requireContext())
+            view.swipeRefresh.setColorSchemeColors(primaryTextColor)
+            swipeRefreshFeature.set(
+                feature = SwipeRefreshFeature(
+                    requireComponents.core.sessionManager,
+                    requireComponents.useCases.sessionUseCases.reload,
+                    view.swipeRefresh,
+                    customTabSessionId
+                ),
+                owner = this,
+                view = view
+            )
+        } else {
+            // Disable pull to refresh
+            view.swipeRefresh.setOnChildScrollUpCallback { _, _ -> true }
+        }
 
         readerViewFeature.set(
             feature = ReaderViewFeature(