[iOS] Prevent Voiceover from reading behind scrim during search

Before, when the scrim was up, dimming the results view, Voiceover
would still read the dimmed elements. Now, as part of putting up the
scrim, the table view marks all its subviews as accessibilityHidden,
so they don't appear in Voiceover. The opposite happens when the scrim
is removed.

Bug: 981343
Change-Id: Ibfb9d37f64c30f75fbe6d05633c7e6f4790f3713
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1826888Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/master@{#700296}

ios/chrome/browser/ui/bookmarks/bookmark_home_view_controller.mm

@@ -1287,6 +1287,7 @@ std::vector<GURL> GetUrlsToOpen(const std::vector<const BookmarkNode*>& nodes) {
   // We attach our constraints to the superview because the tableView is
   // a scrollView and it seems that we get an empty frame when attaching to it.
   AddSameConstraints(self.scrimView, self.view.superview);
+  self.tableView.accessibilityElementsHidden = YES;
   self.tableView.scrollEnabled = NO;
   [UIView animateWithDuration:kTableViewNavigationScrimFadeDuration
                    animations:^{
@@ -1303,6 +1304,7 @@ std::vector<GURL> GetUrlsToOpen(const std::vector<const BookmarkNode*>& nodes) {
       }
       completion:^(BOOL finished) {
         [self.scrimView removeFromSuperview];
+        self.tableView.accessibilityElementsHidden = NO;
         self.tableView.scrollEnabled = YES;
       }];
   [self setupContextBar];

ios/chrome/browser/ui/history/history_table_view_controller.mm

@@ -890,6 +890,7 @@ const CGFloat kButtonHorizontalPadding = 30.0;
     // a scrollView and it seems that we get an empty frame when attaching to
     // it.
     AddSameConstraints(self.scrimView, self.view.superview);
+    self.tableView.accessibilityElementsHidden = YES;
     self.tableView.scrollEnabled = NO;
     [UIView animateWithDuration:kTableViewNavigationScrimFadeDuration
                      animations:^{
@@ -909,6 +910,7 @@ const CGFloat kButtonHorizontalPadding = 30.0;
         }
         completion:^(BOOL finished) {
           [self.scrimView removeFromSuperview];
+          self.tableView.accessibilityElementsHidden = NO;
           self.tableView.scrollEnabled = YES;
         }];
   }

ios/chrome/browser/ui/settings/language/add_language_table_view_controller.mm

@@ -245,6 +245,7 @@ typedef NS_ENUM(NSInteger, ItemType) {
 
 // Shows the scrim overlay.
 - (void)showScrim {
+  self.tableView.accessibilityElementsHidden = YES;
   self.tableView.scrollEnabled = NO;
   [self.tableView addSubview:self.scrimView];
   // Attach constraints to the superview because tableView is a scrollView and
@@ -265,6 +266,7 @@ typedef NS_ENUM(NSInteger, ItemType) {
       }
       completion:^(BOOL finished) {
         [self.scrimView removeFromSuperview];
+        self.tableView.accessibilityElementsHidden = NO;
         self.tableView.scrollEnabled = YES;
       }];
 }

ios/chrome/browser/ui/settings/password/passwords_table_view_controller.mm

@@ -623,6 +623,7 @@ std::vector<std::unique_ptr<autofill::PasswordForm>> CopyOf(
     // a scrollView and it seems that we get an empty frame when attaching to
     // it.
     AddSameConstraints(self.scrimView, self.view.superview);
+    self.tableView.accessibilityElementsHidden = YES;
     self.tableView.scrollEnabled = NO;
     [UIView animateWithDuration:kTableViewNavigationScrimFadeDuration
                      animations:^{
@@ -641,6 +642,7 @@ std::vector<std::unique_ptr<autofill::PasswordForm>> CopyOf(
         }
         completion:^(BOOL finished) {
           [self.scrimView removeFromSuperview];
+          self.tableView.accessibilityElementsHidden = NO;
           self.tableView.scrollEnabled = YES;
         }];
   }