Fix tests in when MD is set to EXPERIMENTAL by default

ash/test/ash_md_test_base.h

Index: ash/test/ash_md_test_base.h
diff --git a/ash/test/ash_md_test_base.h b/ash/test/ash_md_test_base.h
index 51a6186d09399b4b2184985417f7e18320a8af94..1e34a402c733235fc712842bfb8d6d0d062ed45d 100644
--- a/ash/test/ash_md_test_base.h
+++ b/ash/test/ash_md_test_base.h
@@ -24,6 +24,7 @@ class AshMDTestBase
   void TearDown() override;
 
   int GetMdMaximizedWindowHeightOffset();
+  int GetMdAutoHiddenShelfHeightOffset();
 
  private:
   std::unique_ptr<MaterialDesignControllerTestAPI> material_design_state_;
@@ -32,6 +33,10 @@ class AshMDTestBase
   // adjust the expected height of a maximized window.
   int md_maximized_window_height_offset_ = 0;
 
+  // The material design auto hidden shelf is shorter (by 3) so use this offset
+  // to adjust the display/root window size.
+  int md_auto_hidden_shelf_height_offset_ = 0;
+
   DISALLOW_COPY_AND_ASSIGN(AshMDTestBase);
 };