[iOS][Alert] Supports real time dynamic type

Updates the constraints related to dynamic type when the content size
category changes.
Sets all labels and text fields to automatically adjust fot the content
size category.

Bug: 959764, 951300
Change-Id: Ib072e40ef1821e20941740e07f194e5a17ccecdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611604
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Auto-Submit: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659962}

ios/chrome/browser/ui/alert_view_controller/alert_view_controller.mm

@@ -139,15 +139,24 @@ constexpr int kTextfieldBackgroundColor = 0xf7f7f7;
   self.swipeRecognizer.enabled = NO;
   [self.contentView addGestureRecognizer:self.swipeRecognizer];
 
-  BOOL isAccessibilityContentSize =
-      UIContentSizeCategoryIsAccessibilityCategory(
-          [UIApplication sharedApplication].preferredContentSizeCategory);
-  const CGFloat alertWidth =
-      isAccessibilityContentSize ? kAlertWidthAccessibilty : kAlertWidth;
+  auto GetAlertWidth = ^CGFloat(void) {
+    BOOL isAccessibilityContentSize =
+        UIContentSizeCategoryIsAccessibilityCategory(
+            [UIApplication sharedApplication].preferredContentSizeCategory);
+    return isAccessibilityContentSize ? kAlertWidthAccessibilty : kAlertWidth;
+  };
+
   NSLayoutConstraint* widthConstraint =
-      [self.contentView.widthAnchor constraintEqualToConstant:alertWidth];
+      [self.contentView.widthAnchor constraintEqualToConstant:GetAlertWidth()];
   widthConstraint.priority = UILayoutPriorityRequired - 1;
 
+  [[NSNotificationCenter defaultCenter]
+      addObserverForName:UIContentSizeCategoryDidChangeNotification
+                  object:nil
+                   queue:[NSOperationQueue mainQueue]
+              usingBlock:^(NSNotification* _Nonnull note) {
+                widthConstraint.constant = GetAlertWidth();
+              }];
   [NSLayoutConstraint activateConstraints:@[
     widthConstraint,
 
@@ -214,6 +223,7 @@ constexpr int kTextfieldBackgroundColor = 0xf7f7f7;
     UILabel* titleLabel = [[UILabel alloc] init];
     titleLabel.font =
         [UIFont preferredFontForTextStyle:UIFontTextStyleHeadline];
+    titleLabel.adjustsFontForContentSizeCategory = YES;
     titleLabel.textAlignment = NSTextAlignmentCenter;
     titleLabel.text = self.title;
     titleLabel.translatesAutoresizingMaskIntoConstraints = NO;
@@ -232,6 +242,7 @@ constexpr int kTextfieldBackgroundColor = 0xf7f7f7;
     messageLabel.numberOfLines = 0;
     messageLabel.font =
         [UIFont preferredFontForTextStyle:UIFontTextStyleFootnote];
+    messageLabel.adjustsFontForContentSizeCategory = YES;
     messageLabel.textAlignment = NSTextAlignmentCenter;
     messageLabel.text = self.message;
     messageLabel.translatesAutoresizingMaskIntoConstraints = NO;
@@ -315,6 +326,7 @@ constexpr int kTextfieldBackgroundColor = 0xf7f7f7;
       textField.translatesAutoresizingMaskIntoConstraints = NO;
       textField.delegate = self;
       textField.font = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];
+      textField.adjustsFontForContentSizeCategory = YES;
 
       [fieldStack addArrangedSubview:textField];
       ChromeDirectionalEdgeInsets fieldInsets = ChromeDirectionalEdgeInsetsMake(
@@ -353,7 +365,9 @@ constexpr int kTextfieldBackgroundColor = 0xf7f7f7;
       font = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];
       textColor = UIColorFromRGB(kButtonTextDestructiveColor);
     }
-    [button.titleLabel setFont:font];
+    button.titleLabel.font = font;
+    button.titleLabel.adjustsFontForContentSizeCategory = YES;
+
     [button setTitleColor:textColor forState:UIControlStateNormal];
     [button setTitle:action.title forState:UIControlStateNormal];