Fix unused imports in Material Tree example

Author: GZGavinZhao

angular_components/lib/material_select/dropdown_button.dart

@@ -8,11 +8,11 @@ import 'dart:async';
 import 'dart:html';
 
 import 'package:angular/angular.dart';
-import 'package:angular_components/angular_components.dart';
 import 'package:angular_components/button_decorator/button_decorator.dart';
 import 'package:angular_components/focus/focus_interface.dart';
 import 'package:angular_components/focus/keyboard_only_focus_indicator.dart';
 import 'package:angular_components/interfaces/has_disabled.dart';
+import 'package:angular_components/material_icon/material_icon.dart';
 import 'package:angular_components/mixins/button_wrapper.dart';
 import 'package:angular_components/mixins/focusable_mixin.dart';
 import 'package:angular_components/utils/id_generator/id_generator.dart';

angular_components/lib/material_select/material_select_dropdown_item.dart

@@ -7,9 +7,9 @@
 import 'dart:html';
 
 import 'package:angular/angular.dart';
-import 'package:angular_components/angular_components.dart';
 import 'package:angular_components/dynamic_component/dynamic_component.dart';
 import 'package:angular_components/material_checkbox/material_checkbox.dart';
+import 'package:angular_components/material_icon/material_icon.dart';
 import 'package:angular_components/material_select/activation_handler.dart';
 import 'package:angular_components/material_select/handles_aria.dart';
 import 'package:angular_components/material_select/material_select_item.dart';

angular_components/lib/material_select/material_select_item.dart

@@ -9,14 +9,8 @@ import 'dart:html';
 
 import 'package:angular/angular.dart';
 import 'package:angular_components/angular_components.dart';
-import 'package:angular_components/button_decorator/button_decorator.dart';
-import 'package:angular_components/dynamic_component/dynamic_component.dart';
 import 'package:angular_components/interfaces/has_disabled.dart';
-import 'package:angular_components/material_checkbox/material_checkbox.dart';
-import 'package:angular_components/material_select/activation_handler.dart';
-import 'package:angular_components/mixins/material_dropdown_base.dart';
 import 'package:angular_components/model/selection/selection_container.dart';
-import 'package:angular_components/model/selection/selection_model.dart';
 import 'package:angular_components/model/ui/has_factory.dart';
 import 'package:angular_components/utils/disposer/disposer.dart';
 

angular_components/lib/src/material_tree/material_tree_impl.dart

@@ -3,15 +3,12 @@
 // BSD-style license that can be found in the LICENSE file.
 
 // @dart=2.9
-import 'dart:async';
 
 import 'package:angular/angular.dart';
 import 'package:angular_components/model/selection/select.dart';
-import 'package:angular_components/model/selection/selection_container.dart';
 import 'package:angular_components/model/selection/selection_model.dart';
 import 'package:angular_components/model/selection/selection_options.dart';
 import 'package:angular_components/model/ui/has_factory.dart';
-import 'package:angular_components/utils/disposer/disposer.dart';
 
 import 'group/material_tree_group.dart';
 import 'group/material_tree_group_flat.dart';

examples/material_input_example/lib/material_input_demo.dart

@@ -11,7 +11,6 @@ import 'package:angular_components/material_button/material_button.dart';
 import 'package:angular_components/material_icon/material_icon.dart';
 import 'package:angular_components/material_input/material_input.dart';
 import 'package:angular_components/material_input/material_input_auto_select.dart';
-import 'package:angular_components/material_input/material_input_multiline.dart';
 import 'package:angular_components/material_input/material_number_accessor.dart';
 import 'package:angular_components/material_tooltip/material_tooltip.dart';
 

examples/material_select_example/lib/material_dropdown_select_full_demo.dart

@@ -8,7 +8,6 @@ import 'dart:async';
 import 'dart:html';
 
 import 'package:angular/angular.dart';
-import 'package:angular_forms/angular_forms.dart';
 import 'package:angular_components/laminate/enums/alignment.dart';
 import 'package:angular_components/laminate/popup/module.dart';
 import 'package:angular_components/material_checkbox/material_checkbox.dart';