Reland of [multiball] Replace AppDelegate's window with Scene's window.

This is a reland of http://crrev.com/c/1827373.
The original CL broke downstream multitasking fix. This includes a
fix to multitasking tests.

Original description:
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)

Change-Id: Id286f8c8d957504558effdfd1e9d7ac22ad2a23c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1856320Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706389}

ios/chrome/app/BUILD.gn

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

ios/chrome/app/main_application_delegate.mm

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

ios/chrome/app/multitasking_test_application_delegate.mm

@@ -38,16 +38,14 @@ const CGFloat kWidthLandscapeSplitViewOnLargeIPad = 678.0;
 
 - (BOOL)application:(UIApplication*)application
     didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
-  // Configure application window size for multitasking tests.
+  BOOL returnValue = [super application:application
+          didFinishLaunchingWithOptions:launchOptions];
+  // Adjust window size for multitasking tests.
   CGSize newWindowSize = [self windowSize];
-  self.window = [[ChromeOverlayWindow alloc]
-      initWithFrame:CGRectMake(0, 0, newWindowSize.width,
-                               newWindowSize.height)];
+  self.window.frame =
+      CGRectMake(0, 0, newWindowSize.width, newWindowSize.height);
 
-  BOOL inBackground =
-      [application applicationState] == UIApplicationStateBackground;
-  return [[self appState] requiresHandlingAfterLaunchWithOptions:launchOptions
-                                                 stateBackground:inBackground];
+  return returnValue;
 }
 
 // Returns true if test is running on 12.9 inch iPad Pro. Otherwise, it's

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

@@ -21,6 +21,7 @@ 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

@@ -4,6 +4,10 @@
 
 #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
@@ -15,6 +19,14 @@
   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

@@ -4,6 +4,9 @@
 
 #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
@@ -18,7 +21,18 @@
   return _sceneState;
 }
 
-#pragma mark - UISceneDelegate
+#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 Connecting and Disconnecting the Scene
 
@@ -26,6 +40,7 @@
     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

@@ -44,7 +44,9 @@ typedef NS_ENUM(NSUInteger, SceneActivationLevel) {
 @property(nonatomic, assign) SceneActivationLevel activationLevel;
 
 // Window for the associated scene, if any.
-@property(nonatomic, weak) UIWindow* window;
+@property(nonatomic, strong) UIWindow* window;
+
+@property(nonatomic, strong) UIWindowScene* scene API_AVAILABLE(ios(13));
 
 // 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

@@ -5,6 +5,8 @@
 #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."
@@ -26,6 +28,7 @@
 @end
 
 @implementation SceneState
+@synthesize window = _window;
 
 - (instancetype)init {
   self = [super init];
@@ -48,6 +51,30 @@
 
 #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;