Add keyboard overlay help for the Search key as a Function key extended keyboard shortcuts.

chrome/browser/resources/chromeos/keyboard_overlay.css

Index: chrome/browser/resources/chromeos/keyboard_overlay.css
diff --git a/chrome/browser/resources/chromeos/keyboard_overlay.css b/chrome/browser/resources/chromeos/keyboard_overlay.css
index b58b53a0744e5e4411c5f3a90235f02ac083b394..47af98972217ae0209ef6ae8dcce7d527e5611b1 100644
--- a/chrome/browser/resources/chromeos/keyboard_overlay.css
+++ b/chrome/browser/resources/chromeos/keyboard_overlay.css
@@ -89,6 +89,10 @@ body {
   border-color: rgb(184, 84, 84);
 }
 
+.keyboard-overlay-key.is-shortcut.modifier-search {
+  border-color: rgb(204, 204, 80);
+}
+
 .keyboard-overlay-key.is-shortcut.modifier-shift.modifier-ctrl {
   border-color: rgb(121, 172, 143);
 }
@@ -161,6 +165,10 @@ body {
                                                 rgb(80, 36, 27));
 }
 
+.keyboard-overlay-key.pressed.is-search {
+  background: -webkit-linear-gradient(rgb(242, 242, 126), rgb(186, 186, 52));
+}
+
 .keyboard-overlay-shortcut-text {
   -webkit-box-flex: 1;
   -webkit-box-ordinal-group: 1;