Enable MD dynamic refresh on ChromeOS

BUG=881371
R=robliao

Change-Id: Ic4a06e4e98cf93339ee9038d25ee6cc7b945037b
Reviewed-on: https://chromium-review.googlesource.com/c/1277684
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599874}

ui/base/material_design/material_design_controller.cc

@@ -143,7 +143,12 @@ void MaterialDesignController::Initialize() {
                  << "' for command line switch '" << switches::kTopChromeMD
                  << "'.";
     }
+#if defined(OS_CHROMEOS)
+    is_refresh_dynamic_ui_ = true;
+    SetMode(MATERIAL_REFRESH);
+#else
     SetMode(DefaultMode());
+#endif
   }
 
   // Ideally, there would be a more general, "initialize random stuff here"