[WebUI] Update cr-action-menu hover background color

Focused item background color should be changed to
google-grey-200(#e8eaed).

Bug: 842380
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I9a16e764764fa1c908c5aeb0f523b5c9e88ea295
Reviewed-on: https://chromium-review.googlesource.com/1057648
Commit-Queue: Hwanseung Lee <hwanseung@chromium.org>
Reviewed-by: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558464}

ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.html

@@ -51,7 +51,7 @@
       }
 
       :host ::slotted(.dropdown-item:focus) {
-        background-color: var(--paper-grey-300);
+        background-color: var(--google-grey-200);
         outline: none;
       }
 

ui/webui/resources/cr_elements/shared_vars_css.html

@@ -120,6 +120,7 @@
 
     /** MD Refresh Styles */
     --google-blue-600: #1A73E8;
+    --google-grey-200: #E8EAED;
     --google-grey-400: #BDC1C6;
     --google-grey-900: #202124;
   }