[ios] Fix blank secondary text view issue in PopoverLabelViewController

Previously when passing nil to secondaryAttributedString  while
initiating a PopoverLabelViewController, the popover will show a large
blank area under the primary message. That's because a blank secondary
TextView has occupied the space. Fixed the issue by only create
secondary TextView when secondaryAttributedString has a value.

Bug: 1115925
Change-Id: Ic01ae94037aaae14b76194aca439b3677682b921
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354519
Commit-Queue: Tina Wang <tinazwang@chromium.org>
Reviewed-by: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798627}

ios/chrome/common/ui/elements/popover_label_view_controller.mm

@@ -113,6 +113,10 @@ constexpr CGFloat kVerticalDistance = 24;
 
   [_scrollView addSubview:textView];
 
+  // Only create secondary TextView when |secondaryAttributedString| is not nil.
+  // Set the constraint accordingly.
+  if (self.secondaryAttributedString &&
+      !self.secondaryAttributedString.length) {
     UITextView* secondaryTextView = [[UITextView alloc] init];
     secondaryTextView.scrollEnabled = NO;
     secondaryTextView.editable = NO;
@@ -125,29 +129,10 @@ constexpr CGFloat kVerticalDistance = 24;
     secondaryTextView.textColor = [UIColor colorNamed:kTextSecondaryColor];
     secondaryTextView.linkTextAttributes =
         @{NSForegroundColorAttributeName : [UIColor colorNamed:kBlueColor]};
-
-  if (self.secondaryAttributedString) {
     secondaryTextView.attributedText = self.secondaryAttributedString;
-  }
 
     [_scrollView addSubview:secondaryTextView];
 
-  NSLayoutConstraint* heightConstraint = [_scrollView.heightAnchor
-      constraintEqualToAnchor:_scrollView.contentLayoutGuide.heightAnchor
-                   multiplier:1];
-
-  // UILayoutPriorityDefaultHigh is the default priority for content
-  // compression. Setting this lower avoids compressing the content of the
-  // scroll view.
-  heightConstraint.priority = UILayoutPriorityDefaultHigh - 1;
-  heightConstraint.active = YES;
-
-  CGFloat verticalOffset =
-      (secondaryTextView.attributedText) ? -kVerticalDistance : 0;
-  NSLayoutConstraint* verticalConstraint =
-      [textView.bottomAnchor constraintEqualToAnchor:secondaryTextView.topAnchor
-                                            constant:verticalOffset];
-
     [NSLayoutConstraint activateConstraints:@[
       [textContainerView.widthAnchor
           constraintEqualToAnchor:_scrollView.widthAnchor],
@@ -163,13 +148,44 @@ constexpr CGFloat kVerticalDistance = 24;
       [textContainerView.trailingAnchor
           constraintEqualToAnchor:secondaryTextView.trailingAnchor
                          constant:kHorizontalInsetValue],
-    verticalConstraint,
-    [textContainerView.topAnchor constraintEqualToAnchor:textView.topAnchor
+      [textView.bottomAnchor constraintEqualToAnchor:secondaryTextView.topAnchor
+                                            constant:-kVerticalDistance],
+      [textContainerView.topAnchor
+          constraintEqualToAnchor:textView.topAnchor
                          constant:-kVerticalInsetValue],
       [textContainerView.bottomAnchor
           constraintEqualToAnchor:secondaryTextView.bottomAnchor
                          constant:kVerticalInsetValue],
     ]];
+  } else {
+    // Constraints used when only have primary TextView.
+    [NSLayoutConstraint activateConstraints:@[
+      [textContainerView.widthAnchor
+          constraintEqualToAnchor:_scrollView.widthAnchor],
+      [textContainerView.leadingAnchor
+          constraintEqualToAnchor:textView.leadingAnchor
+                         constant:-kHorizontalInsetValue],
+      [textContainerView.trailingAnchor
+          constraintEqualToAnchor:textView.trailingAnchor
+                         constant:kHorizontalInsetValue],
+      [textContainerView.topAnchor
+          constraintEqualToAnchor:textView.topAnchor
+                         constant:-kVerticalInsetValue],
+      [textContainerView.bottomAnchor
+          constraintEqualToAnchor:textView.bottomAnchor
+                         constant:kVerticalInsetValue],
+    ]];
+  }
+
+  NSLayoutConstraint* heightConstraint = [_scrollView.heightAnchor
+      constraintEqualToAnchor:_scrollView.contentLayoutGuide.heightAnchor
+                   multiplier:1];
+
+  // UILayoutPriorityDefaultHigh is the default priority for content
+  // compression. Setting this lower avoids compressing the content of the
+  // scroll view.
+  heightConstraint.priority = UILayoutPriorityDefaultHigh - 1;
+  heightConstraint.active = YES;
 }
 
 - (void)viewWillAppear:(BOOL)animated {