Add MD Ink Drop to host only when a ripple/hover is active.

ui/views/views.gyp

 # Copyright (c) 2012 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.
 {
   'variables': {
     'chromium_code': 1,
     # Sources lists shared with GN build.
     'views_sources': [
       'accessibility/native_view_accessibility.cc',
       'accessibility/native_view_accessibility.h',
@@ skipping 14 matching lines @@
       'animation/ink_drop_animation_controller_impl.h',
       'animation/ink_drop_animation_ended_reason.cc',
       'animation/ink_drop_animation_ended_reason.h',
       'animation/ink_drop_animation_observer.h',
       'animation/ink_drop_delegate.h',
       'animation/ink_drop_host.h',
       'animation/ink_drop_host_view.cc',
       'animation/ink_drop_host_view.h',
       'animation/ink_drop_hover.cc',
       'animation/ink_drop_hover.h',
+      'animation/ink_drop_hover_observer.h',
       'animation/ink_drop_painted_layer_delegates.cc',
       'animation/ink_drop_painted_layer_delegates.h',
       'animation/ink_drop_state.cc',
       'animation/ink_drop_state.h',
       'animation/scroll_animator.cc',
       'animation/scroll_animator.h',
       'animation/flood_fill_ink_drop_animation.cc',
       'animation/flood_fill_ink_drop_animation.h',
       'animation/square_ink_drop_animation.cc',
       'animation/square_ink_drop_animation.h',
@@ skipping 452 matching lines @@
       'animation/test/ink_drop_animation_controller_impl_test_api.h',
       'animation/test/ink_drop_hover_test_api.cc',
       'animation/test/ink_drop_hover_test_api.h',
       'animation/test/square_ink_drop_animation_test_api.cc',
       'animation/test/square_ink_drop_animation_test_api.h',
       'animation/test/test_ink_drop_animation_observer.cc',
       'animation/test/test_ink_drop_animation_observer.h',
       'animation/test/test_ink_drop_animation_observer_helper.h',
       'animation/test/test_ink_drop_host.cc',
       'animation/test/test_ink_drop_host.h',
+      'animation/test/test_ink_drop_hover_observer.cc',
+      'animation/test/test_ink_drop_hover_observer.h',
       'animation/test/test_ink_drop_delegate.cc',
       'animation/test/test_ink_drop_delegate.h',
       'controls/textfield/textfield_test_api.cc',
       'controls/textfield/textfield_test_api.h',
       'test/capture_tracking_view.cc',
       'test/capture_tracking_view.h',
       'test/combobox_test_api.cc',
       'test/combobox_test_api.h',
       'test/desktop_test_views_delegate.h',
       'test/desktop_test_views_delegate_mac.mm',
@@ skipping 510 matching lines @@
                 '../aura/aura.gyp:aura',
                 '../wm/wm.gyp:wm',
               ],
             }],
           ],
         },  # target_name: macviews_interactive_ui_tests
       ],  # targets
     }],
   ],  # conditions
 }