[ios] Fix VoiceOver issue of TableViewInfoButtonCell

Previously the button won't be read and the users can't double tap to
show the popover when voiceover is on.

Bug: 1123788
Change-Id: I0e638b5f14fea8cddd67b1e7c8525b38bfd82c38
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2387151Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Tina Wang <tinazwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804110}

ios/chrome/browser/ui/table_view/cells/table_view_info_button_cell.mm

@@ -305,9 +305,10 @@ const CGFloat kCellLabelsWidthProportion = 0.2f;
 #pragma mark - UIAccessibility
 
 - (CGPoint)accessibilityActivationPoint {
-  // Center the activation point over the button.
+  // Center the activation point over the info button, so that double-tapping
+  // triggers to show the popover.
   CGRect buttonFrame = UIAccessibilityConvertFrameToScreenCoordinates(
-      self.contentView.frame, self);
+      self.trailingButton.frame, self);
   return CGPointMake(CGRectGetMidX(buttonFrame), CGRectGetMidY(buttonFrame));
 }