Gut ash::MaterialDesignController, and remove the about:flags entry.

ash/test/ash_test_base.h

Index: ash/test/ash_test_base.h
diff --git a/ash/test/ash_test_base.h b/ash/test/ash_test_base.h
index 8b81b2be0e72a5dbb4a6a4bac915b93cf813aad2..c819fef2168b789a4b0953fa4bb98ca7752d878a 100644
--- a/ash/test/ash_test_base.h
+++ b/ash/test/ash_test_base.h
@@ -10,7 +10,6 @@
 #include <memory>
 #include <string>
 
-#include "ash/common/material_design/material_design_controller.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/threading/thread.h"
@@ -140,13 +139,6 @@ class AshTestBase : public testing::Test {
 
   void set_start_session(bool start_session) { start_session_ = start_session; }
 
-  // Sets material mode for the test. This will override material mode set via
-  // command line switches.
-  void set_material_mode(MaterialDesignController::Mode material_mode) {
-    CHECK(!setup_called_);
-    material_mode_ = material_mode;
-  }
-
   AshTestHelper* ash_test_helper() { return ash_test_helper_.get(); }
 
   void RunAllPendingInMessageLoop();
@@ -183,7 +175,6 @@ class AshTestBase : public testing::Test {
   bool teardown_called_;
   // |SetUp()| doesn't activate session if this is set to false.
   bool start_session_;
-  MaterialDesignController::Mode material_mode_;
   std::unique_ptr<AshTestEnvironment> ash_test_environment_;
   std::unique_ptr<AshTestHelper> ash_test_helper_;
   std::unique_ptr<ui::test::EventGenerator> event_generator_;