[Mac] Fixed the incognito omnibox icon background color

BUG=588377, 666980

Review-Url: https://codereview.chromium.org/2513083002
Cr-Commit-Position: refs/heads/master@{#433338}
(cherry picked from commit 40b3059)

Review URL: https://codereview.chromium.org/2515193003 .

Cr-Commit-Position: refs/branch-heads/2924@{#31}
Cr-Branched-From: 3a87aec-refs/heads/master@{#433059}

chrome/browser/ui/cocoa/location_bar/location_bar_decoration.mm

@@ -23,9 +23,9 @@
 
 // Color values for the hover and pressed background.
 const SkColor kHoverBackgroundColor = 0x14000000;
-const SkColor kHoverDarkBackgroundColor = 0x1E000000;
+const SkColor kHoverDarkBackgroundColor = 0x1EFFFFFF;
 const SkColor kPressedBackgroundColor = 0x1E000000;
-const SkColor kPressedDarkBackgroundColor = 0x3D000000;
+const SkColor kPressedDarkBackgroundColor = 0x3DFFFFFF;
 
 // Amount of inset for the background frame.
 const CGFloat kBackgroundFrameYInset = 2.0;
@@ -180,7 +180,7 @@ - (void)mouseExited:(NSEvent*)event {
           in_dark_mode ? kHoverDarkBackgroundColor : kHoverBackgroundColor;
     } else {
       background_color =
-          in_dark_mode ? kPressedBackgroundColor : kPressedDarkBackgroundColor;
+          in_dark_mode ? kPressedDarkBackgroundColor : kPressedBackgroundColor;
     }
 
     [skia::SkColorToSRGBNSColor(background_color) setFill];