[ios] Implement text setters in InfobarBannerViewController

This change will be necessary since the Translate Infobar changes
states through the Translate lifecycle, requiring the banner texts
to be update.

Bug: 1014959
Change-Id: I74e908b33e17529dfa3ebd39a636564ce2df2871
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1897909Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712831}

ios/chrome/browser/ui/infobars/banners/infobar_banner_view_controller.mm

@@ -332,6 +332,29 @@ const CGFloat kLongPressTimeDurationInSeconds = 0.4;
   self.shouldDismissAfterTouchesEnded = YES;
 }
 
+#pragma mark - Getters/Setters
+
+- (void)setTitleText:(NSString*)titleText {
+  _titleText = titleText;
+  if (self.titleLabel) {
+    self.titleLabel.text = _titleText;
+  }
+}
+
+- (void)setSubTitleText:(NSString*)subTitleText {
+  _subTitleText = subTitleText;
+  if (self.subTitleLabel) {
+    self.subTitleLabel.text = _subTitleText;
+  }
+}
+
+- (void)setButtonText:(NSString*)buttonText {
+  _buttonText = buttonText;
+  if (self.infobarButton) {
+    [self.infobarButton setTitle:_buttonText forState:UIControlStateNormal];
+  }
+}
+
 #pragma mark - Private Methods
 
 - (void)bannerInfobarButtonWasPressed:(UIButton*)sender {