bug(chips): fixes placeholder in chip inputs #7481 (#7509)

* bug(chips): fixes placeholder in chip inputs #7481

* chore(nit): pr feedback

* chore(tests): fix invalid test

* chore(test): remove 'f'

src/lib/chips/chip-list.spec.ts

@@ -366,9 +366,9 @@ describe('MatChipList', () => {
 
     });
 
-    it('should not float placeholder if no chip is selected', () => {
+    it('should float placeholder if chip is selected', () => {
       expect(formField.classList.contains('mat-form-field-should-float'))
-        .toBe(false, 'placeholder should not be floating');
+        .toBe(true, 'placeholder should be floating');
     });
 
     it('should remove selection if chip has been removed', async(() => {

src/lib/chips/chip-list.ts

@@ -244,7 +244,7 @@ export class MatChipList implements MatFormFieldControl<any>, ControlValueAccess
   }
 
   get shouldPlaceholderFloat(): boolean {
-    return this.empty;
+    return !this.empty || this.focused;
   }
 
   /** Whether this chip-list is disabled. */