[multiball] Make SceneDelegate create and update SceneState.

Creates SceneActivityState enum to list possible scene states and
makes the scene delegate create and update the scene state.

Bug: none
Change-Id: I45932fefcff42828a761b6d4d53fc1c034a3102e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1789524
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695117}

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

@@ -7,11 +7,16 @@
 
 #import <UIKit/UIKit.h>
 
-// An object acting as a scene delegate for UIKit. Updates the window state.
+#import "ios/chrome/browser/ui/main/scene_state.h"
+
+// An object acting as a scene delegate for UIKit. Updates the scene state.
 @interface SceneDelegate : NSObject <UIWindowSceneDelegate>
 
 @property(nonatomic, strong) UIWindow* window;
 
+// The object that holds the state of the scene associated with this delegate.
+@property(nonatomic, strong) SceneState* sceneState;
+
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_MAIN_SCENE_DELEGATE_H_

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

@@ -10,4 +10,46 @@
 
 @implementation SceneDelegate
 
+- (SceneState*)sceneState {
+  if (!_sceneState) {
+    _sceneState = [[SceneState alloc] init];
+  }
+  return _sceneState;
+}
+
+#pragma mark - UISceneDelegate
+
+#pragma mark Connecting and Disconnecting the Scene
+
+- (void)scene:(UIScene*)scene
+    willConnectToSession:(UISceneSession*)session
+                 options:(UISceneConnectionOptions*)connectionOptions
+    API_AVAILABLE(ios(13)) {
+  self.sceneState.activationLevel = SceneActivationLevelBackground;
+}
+
+- (void)sceneDidDisconnect:(UIScene*)scene API_AVAILABLE(ios(13)) {
+  self.sceneState.activationLevel = SceneActivationLevelUnattached;
+}
+
+#pragma mark Transitioning to the Foreground
+
+- (void)sceneWillEnterForeground:(UIScene*)scene API_AVAILABLE(ios(13)) {
+  self.sceneState.activationLevel = SceneActivationLevelForegroundInactive;
+}
+
+- (void)sceneDidBecomeActive:(UIScene*)scene API_AVAILABLE(ios(13)) {
+  self.sceneState.activationLevel = SceneActivationLevelForegroundActive;
+}
+
+#pragma mark Transitioning to the Background
+
+- (void)sceneWillResignActive:(UIScene*)scene API_AVAILABLE(ios(13)) {
+  self.sceneState.activationLevel = SceneActivationLevelForegroundInactive;
+}
+
+- (void)sceneDidEnterBackground:(UIScene*)scene API_AVAILABLE(ios(13)) {
+  self.sceneState.activationLevel = SceneActivationLevelBackground;
+}
+
 @end

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

@@ -7,9 +7,32 @@
 
 #import <UIKit/UIKit.h>
 
+// Describes the possible scene states.
+// This is an iOS 12 compatible version of UISceneActivationState enum.
+typedef NS_ENUM(NSUInteger, SceneActivationLevel) {
+  // The scene is not connected and has no window.
+  SceneActivationLevelUnattached = 0,
+  // The scene is connected, and has a window associated with it. The window is
+  // not visible to the user, except possibly in the app switcher.
+  SceneActivationLevelBackground,
+  // The scene is connected, and its window is on screen, but it's not active
+  // for user input. For example, keyboard events would not be sent to this
+  // window.
+  SceneActivationLevelForegroundInactive,
+  // The scene is connected, has a window, and receives user events.
+  SceneActivationLevelForegroundActive
+};
+
 // An object containing the state of a UIWindowScene. One state object
 // corresponds to one scene.
 @interface SceneState : NSObject
+
+// The current activation level.
+@property(nonatomic, assign) SceneActivationLevel activationLevel;
+
+// Window for the associated scene, if any.
+@property(nonatomic, weak) UIWindow* window;
+
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_MAIN_SCENE_STATE_H_