Revert "[multiball] Replace AppDelegate's window with Scene's window."

This reverts commit 8f80402d.

Reason for revert: broken downstream tests

Original change's description:
> [multiball] Replace AppDelegate's window with Scene's window.
> 
> Adds |window| property to SceneState. It is backed by SceneDelegate's
> |window| property and by UIWindowScene's |scenes| property on iOS 13
> with multiwindow; or with an ivar otherwise. When it's an ivar,
> SceneController is now responsible for window creation.
> Note that the getter for AppDelegate's window remains for iOS 12 compat.
> Note that the window is always a ChromeOverlayWindow.
> 
> have tested it manually on my machine and it still works)
> 
> Bug: none
> Test: verify that the incognito screenshot blocker works as expected (I
> Change-Id: Ic418ece228854e43aa0e4c9d9e503c1b54bca901
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1827373
> Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
> Reviewed-by: Mark Cogan <marq@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#701569}

TBR=marq@chromium.org,stkhapugin@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1012794
Change-Id: I895ea478396be1db4265b8a092d6b12fed76bc5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1849432Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704256}

ios/chrome/app/BUILD.gn

@@ -278,10 +278,8 @@ source_set("app_internal") {
     "MediaPlayer.framework",
   ]
 
-  allow_circular_includes_from = [
-    "//ios/chrome/app/application_delegate:application_delegate_internal",
-    "//ios/chrome/browser/ui/main:scene",
-  ]
+  allow_circular_includes_from =
+      [ "//ios/chrome/app/application_delegate:application_delegate_internal" ]
 }
 
 source_set("mode") {

ios/chrome/app/main_application_delegate.mm

@@ -92,11 +92,14 @@
 }
 
 - (UIWindow*)window {
-  return self.sceneState.window;
+  return [_mainController window];
 }
 
 - (void)setWindow:(UIWindow*)newWindow {
-  NOTREACHED() << "Should not be called, use [SceneState window] instead";
+  DCHECK(newWindow);
+  [_mainController setWindow:newWindow];
+  // self.window has been set by this time. _appState window can now be set.
+  [_appState setWindow:newWindow];
 }
 
 #pragma mark - UIApplicationDelegate methods -
@@ -110,10 +113,9 @@
 - (BOOL)application:(UIApplication*)application
     didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
   startup_loggers::RegisterAppDidFinishLaunchingTime();
-
-  _mainController.window = self.window;
-  // self.window has been set by this time. _appState window can now be set.
-  _appState.window = self.window;
+  // Main window must be ChromeOverlayWindow or a subclass of it.
+  self.window = [[ChromeOverlayWindow alloc]
+      initWithFrame:[[UIScreen mainScreen] bounds]];
 
   BOOL inBackground =
       [application applicationState] == UIApplicationStateBackground;

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

@@ -21,7 +21,6 @@ source_set("scene") {
     "//ios/chrome/browser/tabs:tabs",
     "//ios/chrome/browser/ui/commands:commands",
     "//ios/chrome/browser/ui/tab_grid",
-    "//ios/chrome/browser/ui/util:multiwindow_util",
   ]
 
   libs = [ "UIKit.framework" ]

ios/chrome/browser/ui/main/scene_controller.mm

@@ -4,10 +4,6 @@
 
 #import "ios/chrome/browser/ui/main/scene_controller.h"
 
-#import "base/logging.h"
-#import "ios/chrome/app/chrome_overlay_window.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."
 #endif
@@ -19,14 +15,6 @@
   if (self) {
     _sceneState = sceneState;
     [_sceneState addObserver:self];
-    // The window is necessary very early in the app/scene lifecycle, so it
-    // should be created right away.
-    if (!self.sceneState.window) {
-      DCHECK(!IsMultiwindowSupported())
-          << "The window must be created by the scene delegate";
-      self.sceneState.window = [[ChromeOverlayWindow alloc]
-          initWithFrame:[[UIScreen mainScreen] bounds]];
-    }
   }
   return self;
 }

ios/chrome/browser/ui/main/scene_delegate.mm

@@ -4,9 +4,6 @@
 
 #import "ios/chrome/browser/ui/main/scene_delegate.h"
 
-#include "base/mac/foundation_util.h"
-#import "ios/chrome/app/chrome_overlay_window.h"
-
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
@@ -21,18 +18,7 @@
   return _sceneState;
 }
 
-#pragma mark - UIWindowSceneDelegate
-
-// This getter is called when the SceneDelegate is created. Returning a
-// ChromeOverlayWindow allows UIKit to use that as the main window for this
-// scene.
-- (UIWindow*)window {
-  if (!_window) {
-    // Sizing of the window is handled by UIKit.
-    _window = [[ChromeOverlayWindow alloc] init];
-  }
-  return _window;
-}
+#pragma mark - UISceneDelegate
 
 #pragma mark Connecting and Disconnecting the Scene
 
@@ -40,7 +26,6 @@
     willConnectToSession:(UISceneSession*)session
                  options:(UISceneConnectionOptions*)connectionOptions
     API_AVAILABLE(ios(13)) {
-  self.sceneState.scene = base::mac::ObjCCastStrict<UIWindowScene>(scene);
   self.sceneState.activationLevel = SceneActivationLevelBackground;
 }
 

ios/chrome/browser/ui/main/scene_state.h

@@ -44,9 +44,7 @@ typedef NS_ENUM(NSUInteger, SceneActivationLevel) {
 @property(nonatomic, assign) SceneActivationLevel activationLevel;
 
 // Window for the associated scene, if any.
-@property(nonatomic, strong) UIWindow* window;
-
-@property(nonatomic, strong) UIWindowScene* scene API_AVAILABLE(ios(13));
+@property(nonatomic, weak) UIWindow* window;
 
 // Adds an observer to this scene state. The observers will be notified about
 // scene state changes per SceneStateObserver protocol.

ios/chrome/browser/ui/main/scene_state.mm

@@ -5,8 +5,6 @@
 #import "ios/chrome/browser/ui/main/scene_state.h"
 
 #import "base/ios/crb_protocol_observers.h"
-#import "ios/chrome/app/chrome_overlay_window.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."
@@ -28,7 +26,6 @@
 @end
 
 @implementation SceneState
-@synthesize window = _window;
 
 - (instancetype)init {
   self = [super init];
@@ -51,30 +48,6 @@
 
 #pragma mark - Setters & Getters.
 
-- (void)setWindow:(UIWindow*)window {
-  if (IsMultiwindowSupported()) {
-    // No need to set anything, instead the getter is backed by scene.windows
-    // property.
-    return;
-  }
-  _window = window;
-}
-
-- (UIWindow*)window {
-  if (IsMultiwindowSupported()) {
-    UIWindow* mainWindow = nil;
-    if (@available(ios 13, *)) {
-      for (UIWindow* window in self.scene.windows) {
-        if ([window isKindOfClass:[ChromeOverlayWindow class]]) {
-          mainWindow = window;
-        }
-      }
-    }
-    return mainWindow;
-  }
-  return _window;
-}
-
 - (void)setActivationLevel:(SceneActivationLevel)newLevel {
   if (_activationLevel == newLevel) {
     return;