Change the color of the omnibox button's background

This CL changes the omnibox button's background to match the browsing
mode (incognito or normal).

Bug: 829769
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I052e1228332121e7e75b1b781dabd7c4e6c3083b
Reviewed-on: https://chromium-review.googlesource.com/1012840Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551278}

ios/chrome/browser/ui/toolbar/buttons/toolbar_button_factory.mm

@@ -44,7 +44,7 @@ const int styleCount = 2;
 // Omnibox background.
 const CGFloat kOmniboxBackgroundHeight = 38;
 const CGFloat kOmniboxBackgroundCornerRadius = 13;
-const CGFloat kOmniboxBackgroundAlpha = 0.05;
+const CGFloat kOmniboxButtonBackgroundAlphaFactor = 0.5;
 }  // namespace
 
 @implementation ToolbarButtonFactory
@@ -423,7 +423,8 @@ const CGFloat kOmniboxBackgroundAlpha = 0.05;
   background.translatesAutoresizingMaskIntoConstraints = NO;
   background.userInteractionEnabled = NO;
   background.backgroundColor =
-      [UIColor colorWithWhite:0 alpha:kOmniboxBackgroundAlpha];
+      [self.toolbarConfiguration locationBarBackgroundColorWithVisibility:
+                                     kOmniboxButtonBackgroundAlphaFactor];
   background.layer.cornerRadius = kOmniboxBackgroundCornerRadius;
   [omniboxButton addSubview:background];
   AddSameCenterConstraints(omniboxButton, background);