fix(chips): content not centered vertically on IE in some cases (#13260)

Fixes the chip content not being centered on IE when using a chip avatar. The issue comes from the fact that IE's centering doesn't work if the element has a `min-height`, but not a `height`.

Author: crisbeto

src/lib/chips/chips.scss

@@ -43,6 +43,11 @@ $mat-chip-remove-size: 18px;
   cursor: default;
   min-height: $mat-chip-min-height;
 
+  // Centering the content using flexbox won't work on IE, if we have
+  // a `min-height` without setting a `height`. This height won't do
+  // anything since it's less than the minimum set above.
+  height: 1px;
+
   .mat-chip-remove.mat-icon {
     width: $mat-chip-remove-size;
     height: $mat-chip-remove-size;