[M118 Merge][ntp-modules] V2 GM2 module default colors

Fixes the GM2 default color assigned values for the NTP v2 modules UI.
Specifically the module background in dark mode is assigned a color that
does not match the NTP background color nor the module item background
color.

Before: https://drive.google.com/file/d/1Qaka6-BAWNRGhP6FLZQfypq-Ub-lTYUE/view?usp=drive_link

After:
Variant B - https://drive.google.com/file/d/1u4--DaCGoeAU_RNWk_wtWRE_PLki4luo/view?usp=drive_link
Variant A - https://drive.google.com/file/d/1y6-1i20iw8obqwdWiIPRku7YWqbg26K4/view?usp=drive_link
CWS:
https://drive.google.com/file/d/19wXu1zvnQN06fxrZbH0Ikxh8lo_5Za-q/view?usp=drive_link
https://drive.google.com/file/d/15-VKGE0zIoTq3Co7SRKgIdkpIestOzbL/view?usp=drive_link


(cherry picked from commit 01d0878)

Bug: 1491501
Change-Id: I2dc0ba38bffaf2a6799c2ea6a4ed11d5e5b46c04
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4933219
Reviewed-by: Marlon Facey <mfacey@chromium.org>
Commit-Queue: Roman Arora <romanarora@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1208661}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4938110
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/5993@{#1275}
Cr-Branched-From: 5113507-refs/heads/main@{#1192594}

chrome/browser/ui/color/new_tab_page_color_mixer.cc

@@ -442,7 +442,7 @@ void AddWebThemeNewTabPageColors(ui::ColorMixer& mixer, bool dark_mode) {
 
   if (base::FeatureList::IsEnabled(ntp_features::kNtpModulesRedesigned)) {
     if (dark_mode) {
-      mixer[kColorNewTabPageModuleBackground] = {kColorNewTabPageBackground};
+      mixer[kColorNewTabPageModuleBackground] = {gfx::kGoogleGrey800};
     } else {
       mixer[kColorNewTabPageModuleBackground] = {gfx::kGoogleGrey100};
     }