Pin keyboard matches red lines (go/cros-quick-unlock-ux).

chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.js

Index: chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.js
diff --git a/chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.js b/chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.js
index dfc111d4c5fcd7c32df8aa1e7a95762d0894bfbb..ca343b2e90386434eff0b825f3037bc075960652 100644
--- a/chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.js
+++ b/chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.js
@@ -84,5 +84,13 @@ Polymer({
       event.preventDefault();
       return;
     }
+  },
+
+  /**
+   * Changes the color of the submit button if PIN is ready.
+   * @param {string} value
+   */
+  computeSubmitClass_: function(value) {
+    return value.length > 0 ? 'ready-background' : '';
   }
 });