[ios] Adds visual effect to Disclosure HeaderFooterView

The background added for optimization to DisclosureHeaderFooterView
was removing the VisualEffect being set in the parent class. This CL
moves the optimization background to the parent class in case there's
no visual effect being set.

Bug: 865890
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I7b50ed65fc47c93b6548ca2eb60bd139071c8f28
Reviewed-on: https://chromium-review.googlesource.com/1171856Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582688}

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

@@ -45,9 +45,6 @@ constexpr float kRotationNinetyCCW = -(90 / 180.0) * M_PI;
   DisclosureDirection direction =
       self.collapsed ? DisclosureDirectionUp : DisclosureDirectionDown;
   [header setInitialDirection:direction];
-  // Use colors from styler if available.
-  if (styler.tableViewBackgroundColor)
-    header.contentView.backgroundColor = styler.tableViewBackgroundColor;
   if (styler.headerFooterTitleColor)
     header.titleLabel.textColor = styler.headerFooterTitleColor;
 }

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

@@ -25,9 +25,18 @@
   DCHECK([headerFooter class] == self.cellClass);
   headerFooter.accessibilityTraits = self.accessibilityTraits;
   headerFooter.accessibilityIdentifier = self.accessibilityIdentifier;
-  UIVisualEffectView* visualEffect = [[UIVisualEffectView alloc]
-      initWithEffect:styler.tableViewSectionHeaderBlurEffect];
-  headerFooter.backgroundView = visualEffect;
+  // Use the styler tableViewSectionHeaderBlurEffect if available, if not use
+  // the styler tableViewBackgroundColor (as a performance optimization) if
+  // available.
+  if (styler.tableViewSectionHeaderBlurEffect) {
+    UIVisualEffectView* visualEffect = [[UIVisualEffectView alloc]
+        initWithEffect:styler.tableViewSectionHeaderBlurEffect];
+    headerFooter.backgroundView = visualEffect;
+  } else if (styler.tableViewBackgroundColor) {
+    UIView* backgroundView = [[UIView alloc] init];
+    backgroundView.backgroundColor = styler.tableViewBackgroundColor;
+    headerFooter.backgroundView = backgroundView;
+  }
 }
 
 - (CGFloat)headerHeightForWidth:(CGFloat)width {