MD Buttons: Don't add layers for hidden -> hidden transitions.

ui/views/animation/test/test_ink_drop_host.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_VIEWS_ANIMATION_TEST_TEST_INK_DROP_HOST_H_
 #define UI_VIEWS_ANIMATION_TEST_TEST_INK_DROP_HOST_H_
 
 #include "base/macros.h"
 #include "ui/views/animation/ink_drop_host.h"
 
 namespace views {
 
 // A non-functional implementation of an InkDropHost that can be used during
 // tests.  Tracks the number of hosted ink drop layers.
 class TestInkDropHost : public InkDropHost {
  public:
   TestInkDropHost();
   ~TestInkDropHost() override;
 
-  int num_ink_drop_layers() const { return num_ink_drop_layers_; }
+  int num_ink_drop_layers_added() const { return num_ink_drop_layers_added_; }
+  int num_ink_drop_layers() const {
+    return num_ink_drop_layers_added_ - num_ink_drop_layers_removed_;
+  }
 
   void set_should_show_highlight(bool should_show_highlight) {
     should_show_highlight_ = should_show_highlight;
   }
 
   void set_disable_timers_for_test(bool disable_timers_for_test) {
     disable_timers_for_test_ = disable_timers_for_test;
   }
 
   void set_ripple_overrides_highlight(bool overrides_highlight) {
     ripple_overrides_highlight_ = overrides_highlight;
   }
 
   // TestInkDropHost:
   void AddInkDropLayer(ui::Layer* ink_drop_layer) override;
   void RemoveInkDropLayer(ui::Layer* ink_drop_layer) override;
   std::unique_ptr<InkDropRipple> CreateInkDropRipple() const override;
   std::unique_ptr<InkDropHighlight> CreateInkDropHighlight() const override;
 
  private:
-  int num_ink_drop_layers_;
+  int num_ink_drop_layers_added_;
+  int num_ink_drop_layers_removed_;
 
   bool should_show_highlight_;
 
   bool ripple_overrides_highlight_;
 
   // When true, the InkDropRipple/InkDropHighlight instances will have their
   // timers disabled after creation.
   bool disable_timers_for_test_;
 
   DISALLOW_COPY_AND_ASSIGN(TestInkDropHost);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_ANIMATION_TEST_TEST_INK_DROP_HOST_H_