Autofill: Make the iOS nameForAutofill() match Blink.

ios/web/web_state/js/resources/common.js

Index: ios/web/web_state/js/resources/common.js
diff --git a/ios/web/web_state/js/resources/common.js b/ios/web/web_state/js/resources/common.js
index 8aa4ad3168361120d7718d959a571ed16d4f5865..4bded3ad7bd20ed4163ecb0a68ff7ebaa28fc2ec 100644
--- a/ios/web/web_state/js/resources/common.js
+++ b/ios/web/web_state/js/resources/common.js
@@ -428,14 +428,6 @@ new function() {
     if (trimmedName) {
       return __gCrWeb.common.trim(trimmedName);
     }
-    trimmedName = element.getAttribute('autocomplete');

[Lei Zhang, 2015/05/09 01:46:53]

https://chromereviews.googleplex.com/19497013 which added this is wrong IMO due
to the incorrect changes it made to the autocomplete_attribute_invalid test
expectations.

__gCrWeb.autofill.webFormControlElementToFormField() also calls
element.getAttribute('autocomplete') and all the autocomplete_attribute
heuristics tests passes at ToT. Perhaps it was broken before, so Jim felt this
was the correct solution, but it's simply not needed now.

-    if (trimmedName && trimmedName !== 'off') {
-      return __gCrWeb.common.trim(trimmedName);
-    }
-    trimmedName = element.getAttribute('placeholder');

[Lei Zhang, 2015/05/09 01:46:53]

For placeholder, AKA crbug.com/325206, upstream eventually implemented the same
feature in https://codereview.chromium.org/675883002, which then got ported to
autofill_controller.js in https://chromereviews.googleplex.com/112877013. The
20_checkout_staples.com.html test case would fail if we didn't consider the
placeholder attribute.

-    if (trimmedName) {
-      return __gCrWeb.common.trim(trimmedName);
-    }
     return '';
   };