Use a different icon for the web store under Chromium than Google Chrome.

chrome/browser/resources/ntp/apps.css

 /* Apps */
 
 #apps-content {
   position: relative;
   width: intrinsic;
   max-width: 780px;  /* (124 + margin * 2) * 6 */
 }
 
 html.apps-promo-visible #apps-content {
   max-width: 650px; /* (124 + margin * 2) * 5 */
@@ skipping 95 matching lines @@
 html[install-animation-enabled=true] .app[new=new] {
   opacity: 0;
 }
 
 html[install-animation-enabled=true] .app[new=installed] {
   -webkit-animation: bounce .5s ease-in-out;
   -webkit-transition: opacity .5s;
 }
 
 .app[app-id=web-store-entry] > a {
-  background-image: url("web_store_icon.png");
+  background-image: url("chrome://theme/IDR_WEBSTORE_ICON");
 }
 
 menu > button.default {
   font-weight: bold;
 }
 
 #apps-promo {
   display: none;
 }
 
@@ skipping 50 matching lines @@
 */
 .app[app-id=web-store-entry].loner {
   position: absolute;
   left: 100%;
   top: 0;
 }
 
 html[dir=rtl] .app[app-id=web-store-entry].loner {
   right: 100%;
 }