[multiball] Force browser-based fullscreen in multiwindow.

Forces ShouldScopeFullscreenControllerToBrowser to be enabled when in
multiwindow. This greatly improves usability with multiwindow.

Bug: 1069752, 1060653
Change-Id: I4521b4814ebd42aaadbe27c5252a8ef710928d11
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144108Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758238}

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -890,11 +890,6 @@ NSString* const kBrowserViewControllerSnackbarCategory =
     return;
   _broadcasting = broadcasting;
 
-  if (IsMultiwindowSupported()) {
-    // TODO(crbug.com/1060653): fix fullscreen.
-    return;
-  }
-
   ChromeBroadcaster* broadcaster = self.fullscreenController->broadcaster();
   if (_broadcasting) {
     _toolbarUIUpdater = [[LegacyToolbarUIUpdater alloc]

ios/chrome/browser/ui/fullscreen/BUILD.gn

@@ -39,6 +39,7 @@ source_set("feature_flags") {
   deps = [
     "//base",
     "//components/flags_ui",
+    "//ios/chrome/browser/ui/util:multiwindow_util",
   ]
 }
 

ios/chrome/browser/ui/fullscreen/fullscreen_features.mm

@@ -6,6 +6,7 @@
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
+#import "ios/chrome/browser/ui/util/multi_window_support.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ -25,6 +26,10 @@ bool ShouldUseSmoothScrolling() {
 }
 
 bool ShouldScopeFullscreenControllerToBrowser() {
+  if (IsMultiwindowSupported()) {
+    return true;
+  }
+
   return base::FeatureList::IsEnabled(kFullscreenControllerBrowserScoped);
 }