Initialize _focusLastChipOnBackspace correctly

Author: gioragutt

src/material/chips/chip-list.ts

@@ -131,7 +131,7 @@ export class MatChipList extends _MatChipListMixinBase implements MatFormFieldCo
   private _chipRemoveSubscription: Subscription | null;
 
   /** Used to prevent focus moving to chips while user is holding backspace */
-  private _focusLastChipOnBackspace = false;
+  private _focusLastChipOnBackspace: boolean;
 
   /** The chip input to add more chips */
   protected _chipInput: MatChipTextControl;
@@ -418,10 +418,10 @@ export class MatChipList extends _MatChipListMixinBase implements MatFormFieldCo
     this._dropSubscriptions();
   }
 
-
   /** Associates an HTML input element with this chip list. */
   registerInput(inputElement: MatChipTextControl): void {
     this._chipInput = inputElement;
+    this._focusLastChipOnBackspace = inputElement.empty;
   }
 
   /**