Update mixins to avoid compilation issues

The following 2 issues appears internally:
microsoft/TypeScript#15870
microsoft/TypeScript#9944

Change-Id: I60b669846447ff7f54e7b0f741402333c2b59653

polygerrit-ui/app/elements/shared/gr-autocomplete-dropdown/gr-autocomplete-dropdown.ts

@@ -25,6 +25,7 @@ import {htmlTemplate} from './gr-autocomplete-dropdown_html';
 import {KeyboardShortcutMixin} from '../../../mixins/keyboard-shortcut-mixin/keyboard-shortcut-mixin';
 import {IronFitMixin} from '../../../mixins/iron-fit-mixin/iron-fit-mixin';
 import {customElement, property, observe} from '@polymer/decorators';
+import {IronFitBehavior} from '@polymer/iron-fit-behavior/iron-fit-behavior';
 
 // TODO(TS): Update once GrCursorManager is upated
 export interface GrAutocompleteDropdown {
@@ -55,7 +56,8 @@ interface Item {
 export class GrAutocompleteDropdown extends IronFitMixin(
   KeyboardShortcutMixin(
     GestureEventListeners(LegacyElementMixin(PolymerElement))
-  )
+  ),
+  IronFitBehavior as IronFitBehavior
 ) {
   static get template() {
     return htmlTemplate;

polygerrit-ui/app/elements/shared/gr-overlay/gr-overlay.ts

@@ -21,6 +21,7 @@ import {PolymerElement} from '@polymer/polymer/polymer-element';
 import {htmlTemplate} from './gr-overlay_html';
 import {IronOverlayMixin} from '../../../mixins/iron-overlay-mixin/iron-overlay-mixin';
 import {customElement, property} from '@polymer/decorators';
+import {IronOverlayBehavior} from '@polymer/iron-overlay-behavior/iron-overlay-behavior';
 
 const AWAIT_MAX_ITERS = 10;
 const AWAIT_STEP = 5;
@@ -34,7 +35,8 @@ declare global {
 
 @customElement('gr-overlay')
 export class GrOverlay extends IronOverlayMixin(
-  GestureEventListeners(LegacyElementMixin(PolymerElement))
+  GestureEventListeners(LegacyElementMixin(PolymerElement)),
+  IronOverlayBehavior as IronOverlayBehavior
 ) {
   static get template() {
     return htmlTemplate;

polygerrit-ui/app/mixins/iron-fit-mixin/iron-fit-mixin.ts

@@ -22,8 +22,19 @@ import {Constructor} from '../../utils/common-util';
 
 // The mixinBehaviors clears all type information about superClass.
 // As a workaround, we define IronFitMixin with correct type.
+// Due to the following issues:
+// https://github.com/microsoft/TypeScript/issues/15870
+// https://github.com/microsoft/TypeScript/issues/9944
+// we have to import IronFitBehavior in the same file where IronFitMixin
+// is used. To ensure that this import can't be avoided, the second parameter
+// is added. Usage example:
+// class Element extends IronFitMixin(PolymerElement, IronFitBehavior as IronFitBehavior)
+// The code 'IronFitBehavior as IronFitBehavior' required, becuase IronFitBehavior
+// defined as an object, not as IronFitBehavior instance.
+
 export const IronFitMixin = <T extends Constructor<PolymerElement>>(
-  superClass: T
+  superClass: T,
+  _: IronFitBehavior
 ): T & Constructor<IronFitBehavior> =>
   // TODO(TS): mixinBehaviors in some lib is returning: `new () => T` instead
   // which will fail the type check due to missing IronFitBehavior interface

polygerrit-ui/app/mixins/iron-overlay-mixin/iron-overlay-mixin.ts

@@ -22,9 +22,20 @@ import {Constructor} from '../../utils/common-util';
 
 // The mixinBehaviors clears all type information about superClass.
 // As a workaround, we define IronOverlayMixin with correct type.
+// Due to the following issues:
+// https://github.com/microsoft/TypeScript/issues/15870
+// https://github.com/microsoft/TypeScript/issues/9944
+// we have to import IronOverlayBehavior in the same file where IronOverlayMixin
+// is used. To ensure that this import can't be avoided, the second parameter
+// is added. Usage example:
+// class Element extends IronOverlayMixin(PolymerElement, IronOverlayBehavior as IronOverlayBehavior)
+// The code 'IronOverlayBehavior as IronOverlayBehavior' required, because
+// IronOverlayBehavior defined as an object, not as IronOverlayBehavior instance.
 export const IronOverlayMixin = <T extends Constructor<PolymerElement>>(
-  superClass: T
+  superClass: T,
+  _: IronOverlayBehavior
 ): T & Constructor<IronOverlayBehavior> =>
-  // TODO(TS): mixinBehaviors in some lib is returning: `new () => T` instead
-  // which will fail the type check due to missing IronOverlayBehavior interface
+  // TODO(TS): mixinBehaviors in some lib is returning: `new () => T`
+  // instead which will fail the type check due to missing
+  // IronOverlayBehavior interface
   mixinBehaviors([IronOverlayBehavior], superClass) as any;