add focus method to button base

Author: andrewseguin

src/dev-app/mdc-button/mdc-button-demo.ts

@@ -15,4 +15,7 @@ import {Component} from '@angular/core';
   styleUrls: ['mdc-button-demo.css'],
 })
 export class MdcButtonDemo {
+  isDisabled: boolean = false;
+  clickCounter: number = 0;
+  toggleDisable: boolean = false;
 }

src/material-experimental/mdc-button/button-base.ts

@@ -108,14 +108,19 @@ export class MatButtonBase extends _MatButtonBaseMixin implements CanDisable, Ca
     }
   }
 
+  /** Focuses the button. */
+  focus(): void {
+    this._elementRef.nativeElement.focus();
+  }
+
   /** Gets whether the button has one of the given attributes. */
   private _hasHostAttributes(...attributes: string[]) {
     return attributes.some(attribute => this._elementRef.nativeElement.hasAttribute(attribute));
   }
 }
 
 /** Shared inputs by buttons using the `<a>` tag */
-export const MAT_ANCHOR_INPUTS = MAT_BUTTON_INPUTS.concat(['tabIndex]']);
+export const MAT_ANCHOR_INPUTS = ['disabled', 'disableRipple', 'color', 'tabIndex'];
 
 /** Shared host configuration for buttons using the `<a>` tag. */
 export const MAT_ANCHOR_HOST = {