Change unified system tray colors.

According to the updated UnfiiedSystemTray spec, #F1F3F4 is the correct
color for icons and label texts instead of #F1F2F3.

TEST=manual
BUG=836255

Change-Id: I7e12ac297e69cebe8db7704ef59f99dec9845729
Reviewed-on: https://chromium-review.googlesource.com/1027571Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553862}

ash/system/tray/tray_constants.h

@@ -130,8 +130,8 @@ constexpr SkColor kUnifiedMenuBackgroundColor = SkColorSetRGB(0x20, 0x21, 0x24);
 constexpr SkColor kUnifiedMenuBackgroundColorWithBlur =
     SkColorSetA(kUnifiedMenuBackgroundColor, 0xB3);
 constexpr float kUnifiedMenuBackgroundBlur = 30.f;
-constexpr SkColor kUnifiedMenuTextColor = SkColorSetRGB(0xf1, 0xf2, 0xf3);
-constexpr SkColor kUnifiedMenuIconColor = SkColorSetRGB(0xf1, 0xf2, 0xf3);
+constexpr SkColor kUnifiedMenuTextColor = SkColorSetRGB(0xf1, 0xf3, 0xf4);
+constexpr SkColor kUnifiedMenuIconColor = SkColorSetRGB(0xf1, 0xf3, 0xf4);
 constexpr SkColor kUnifiedMenuSecondaryTextColor =
     SkColorSetA(kUnifiedMenuIconColor, 0xa3);
 constexpr SkColor kUnifiedMenuIconColorDisabled =