[CrOS Settings] Allow zooming in and out on Screen lock pin setup.

Currently, ctrl+= (zoom in) and ctrl+- (zoom out) are ignored while
the Screen lock pin keyboard dialog is onscreen.  This CL ensures that
when the user hits '-' or '=' with ctrl on, zoom in and zoom out occurs.

Fixed: 1032527
Change-Id: I4e0e79bb732b05bc15508e8668e32022efc1ddd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1976904Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Regan Hsu <hsuregan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726622}

ui/webui/resources/cr_components/chromeos/quick_unlock/pin_keyboard.js

@@ -413,6 +413,11 @@ Polymer({
       return true;
     }
 
+    // Valid if the key is CTRL+- or CTRL+= to zoom in and out of the screen.
+    if ((event.keyCode == 187 || event.keyCode == 189) && event.ctrlKey) {
+      return true;
+    }
+
     // The rest of the keys are invalid.
     return false;
   },