Download home: Uses material gear setting icon.

The CL changes the gear icon to use the material asset.

Bug: 864867
Change-Id: I8f37ec3c15a7173b703d88be7a1a7770398eb83b
Reviewed-on: https://chromium-review.googlesource.com/1148892Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577680}

chrome/android/java/res/menu/download_manager_menu.xml

@@ -31,10 +31,9 @@
      </group>
     <group android:id="@+id/with_settings_normal_menu_group"
         android:visible="false" >
-        <!-- TODO(xingliu): Use the new settings icon with better alpha value. -->
         <item
             android:id="@+id/settings_menu_id"
-            android:icon="@drawable/btn_settings"
+            android:icon="@drawable/settings_cog"
             android:title="@string/preferences"
             android:visible="false"
             app:showAsAction="ifRoom"