Add upstream bits necessary for iOS card unmask prompt.

components/autofill/ios/browser/js_autofill_manager.mm

Index: components/autofill/ios/browser/js_autofill_manager.mm
diff --git a/components/autofill/ios/browser/js_autofill_manager.mm b/components/autofill/ios/browser/js_autofill_manager.mm
index 104cff509eaef7bc59cad9891be023378e2149a5..a8938570aece9ddc864360e52dd059a6b6f3737c 100644
--- a/components/autofill/ios/browser/js_autofill_manager.mm
+++ b/components/autofill/ios/browser/js_autofill_manager.mm
@@ -47,6 +47,11 @@
   return @"__gCrWeb.autofill";
 }
 
+- (void)storeActiveElement {
+  NSString* js = @"__gCrWeb.autofill.storeActiveElement()";
+  [self evaluate:js stringResultHandler:nil];
+}
+
 - (void)fillActiveFormField:(NSString*)dataString
           completionHandler:(ProceduralBlock)completionHandler {
   web::JavaScriptCompletion resultHandler = ^void(NSString*, NSError*) {