[ntp] Fix MV tile button color

MV tile button color should follow the NTP theme. However, during
refactoring we made the tile button color follow the OS mode. This CL
reverts the relevant changes.

Bug: 1168368
Change-Id: Ied5b56c5774e359b7c674b54786079bf0ec3a0a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2638858
Auto-Submit: Tibor Goldschwendt <tiborg@chromium.org>
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Reviewed-by: Yue Zhang <yuezhanggg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845194}

chrome/browser/resources/new_tab_page/app.html

@@ -89,6 +89,8 @@
   }
 
   ntp-most-visited[dark] {
+    --icon-button-color-active: var(--google-grey-refresh-300);
+    --icon-button-color: white;
     --tile-hover-color: rgba(255, 255, 255, .1);
   }
 

chrome/browser/resources/new_tab_page/most_visited.html

 <style include="cr-hidden-style cr-icons">
   :host {
+    --icon-button-color-active: var(--google-grey-refresh-700);
+    --icon-button-color: var(--google-grey-600);
     --icon-size: 48px;
     --tile-hover-color: rgba(var(--google-grey-900-rgb), .1);
     --tile-size: 112px;  /* top padding + icon + title margin + title */
@@ -161,7 +163,7 @@
   }
 
   cr-icon-button {
-    --cr-icon-button-fill-color: var(--ntp-icon-button-color);
+    --cr-icon-button-fill-color: var(--icon-button-color);
     --cr-icon-button-size: 28px;
     --cr-icon-button-transition: none;
     margin: 4px 2px;
@@ -187,7 +189,7 @@
   :host-context(.focus-outline-visible):host(:not([reordering_]))
       cr-icon-button:focus,
   :host(:not([reordering_])) cr-icon-button:hover {
-    --cr-icon-button-fill-color: var(--ntp-icon-button-color-active);
+    --cr-icon-button-fill-color: var(--icon-button-color-active);
     opacity: 1;
     transition-delay: 0s;
   }