Add (a no-op) loadPage action to iOS autofill automation.

The Autofill Recorder Extension records an action when a new page is
loaded as part of a button/link click, etc (in addition to the action
that performs that click).

I found that desktop no-ops this action, and that on iOS it also does
not need to be explicitly replayed, so I no-op it here as well. I am
discussing with Yiming the reason it is no-op'd on desktop, and will
add that information here when I receive it.

Change-Id: If5a2f49cf60995831dfae357c97de28266771ea2
Reviewed-on: https://chromium-review.googlesource.com/c/1307994Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: ericale <ericale@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604061}

ios/chrome/browser/autofill/automation/automation_action.mm

@@ -112,6 +112,18 @@ using web::test::ElementSelector;
 @interface AutomationActionSelectDropdown : AutomationAction
 @end
 
+// An action that loads a web page.
+// This is recorded in tandem with the actions that cause loads to
+// occur (i.e. clicking on a link); therefore, this action is
+// a no-op when replaying.
+// We assume this action has a format resembling:
+// {
+//   "url": "www.google.com",
+//   "type": "loadPage"
+// }
+@interface AutomationActionLoadPage : AutomationAction
+@end
+
 @implementation AutomationAction
 
 + (instancetype)actionWithValueDictionary:
@@ -134,6 +146,7 @@ using web::test::ElementSelector;
     @"autofill" : [AutomationActionAutofill class],
     @"validateField" : [AutomationActionValidateField class],
     @"select" : [AutomationActionSelectDropdown class],
+    @"loadPage" : [AutomationActionLoadPage class],
     // More to come.
   };
 
@@ -247,6 +260,14 @@ using web::test::ElementSelector;
 
 @end
 
+@implementation AutomationActionLoadPage
+
+- (void)execute {
+  // loadPage is a no-op action - perform nothing
+}
+
+@end
+
 @implementation AutomationActionWaitFor
 
 - (void)execute {