perf(int-bar): Convert MatInkBarFoundation adapter to class object (#19986)

* perf(int-bar): Convert MatInkBarFoundation adapter to class object

Converts the adapter to class object to hopefully reduce memory usage. Adds getters to access private fields.

* refactor(ink-bar): expose some fields and make public; remove getter methods

* fix(ink-bar): fix build/typing issues in reassigning fields due to readonly

Author: ngwattcos

src/material-experimental/mdc-tabs/ink-bar.ts

@@ -13,6 +13,30 @@ import {
   MDCTabIndicatorFoundation
 } from '@material/tab-indicator';
 
+class TabIndicatorAdapter implements MDCTabIndicatorAdapter {
+  constructor(private readonly _delegate: MatInkBarFoundation) {}
+  addClass(className: string) {
+    if (!this._delegate._destroyed) {
+      this._delegate._hostElement.classList.add(className);
+    }
+  }
+  removeClass(className: string) {
+    if (!this._delegate._destroyed) {
+      this._delegate._hostElement.classList.remove(className);
+    }
+  }
+  setContentStyleProperty(propName: string, value: string | null) {
+    this._delegate._inkBarContentElement.style.setProperty(propName, value);
+  }
+  computeContentClientRect() {
+    // `getBoundingClientRect` isn't available on the server.
+    return this._delegate._destroyed ||
+      !this._delegate._inkBarContentElement.getBoundingClientRect ? {
+      width: 0, height: 0, top: 0, left: 0, right: 0, bottom: 0
+    } : this._delegate._inkBarContentElement.getBoundingClientRect();
+  }
+}
+
 /**
  * Item inside a tab header relative to which the ink bar can be aligned.
  * @docs-private
@@ -62,34 +86,15 @@ export class MatInkBar {
  * @docs-private
  */
 export class MatInkBarFoundation {
-  private _destroyed: boolean;
+  readonly _destroyed: boolean;
   private _foundation: MDCTabIndicatorFoundation;
   private _inkBarElement: HTMLElement;
-  private _inkBarContentElement: HTMLElement;
+  readonly _inkBarContentElement: HTMLElement;
   private _fitToContent = false;
-  private _adapter: MDCTabIndicatorAdapter = {
-    addClass: className => {
-      if (!this._destroyed) {
-        this._hostElement.classList.add(className);
-      }
-    },
-    removeClass: className => {
-      if (!this._destroyed) {
-        this._hostElement.classList.remove(className);
-      }
-    },
-    setContentStyleProperty: (propName, value) => {
-      this._inkBarContentElement.style.setProperty(propName, value);
-    },
-    computeContentClientRect: () => {
-      // `getBoundingClientRect` isn't available on the server.
-      return this._destroyed || !this._inkBarContentElement.getBoundingClientRect ? {
-        width: 0, height: 0, top: 0, left: 0, right: 0, bottom: 0
-      } : this._inkBarContentElement.getBoundingClientRect();
-    }
-  };
+  private _adapter: MDCTabIndicatorAdapter;
 
-  constructor(private _hostElement: HTMLElement, private _document: Document) {
+  constructor(readonly _hostElement: HTMLElement, private _document: Document) {
+    this._adapter = new TabIndicatorAdapter(this);
     this._foundation = new MDCSlidingTabIndicatorFoundation(this._adapter);
   }
 
@@ -120,9 +125,10 @@ export class MatInkBarFoundation {
       this._inkBarElement.parentNode.removeChild(this._inkBarElement);
     }
 
-    this._hostElement = this._inkBarElement = this._inkBarContentElement = null!;
+    (this as {_hostElement: HTMLElement})._hostElement = this._inkBarElement
+      = (this as {_inkBarContentElement: HTMLElement})._inkBarContentElement = null!;
     this._foundation.destroy();
-    this._destroyed = true;
+    (this as {_destroyed: boolean})._destroyed = true;
   }
 
   /**
@@ -148,7 +154,8 @@ export class MatInkBarFoundation {
   /** Creates and appends the ink bar element. */
   private _createInkBarElement() {
     this._inkBarElement = this._document.createElement('span');
-    this._inkBarContentElement = this._document.createElement('span');
+    (this as {_inkBarContentElement: HTMLElement})._inkBarContentElement
+      = this._document.createElement('span');
 
     this._inkBarElement.className = 'mdc-tab-indicator';
     this._inkBarContentElement.className = 'mdc-tab-indicator__content' +