[ios] Use new JS execution API for Autofill.

components/autofill/ios/browser/js_suggestion_manager.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "components/autofill/ios/browser/js_suggestion_manager.h"
 
 #include "base/format_macros.h"
 #include "base/json/string_escape.h"
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 17 matching lines @@
 }
 
 - (void)selectNextElement {
   [self selectElementAfterForm:@"" field:@""];
 }
 
 - (void)selectElementAfterForm:(NSString*)formName field:(NSString*)fieldName {
   NSString* selectNextElementJS = [NSString
       stringWithFormat:@"__gCrWeb.suggestion.selectNextElement(%@, %@)",
                        JSONEscape(formName), JSONEscape(fieldName)];
-  [self evaluate:selectNextElementJS stringResultHandler:nil];
+  [self executeJavaScript:selectNextElementJS completionHandler:nil];
 }
 
 - (void)selectPreviousElement {
   [self selectElementBeforeForm:@"" field:@""];
 }
 
 - (void)selectElementBeforeForm:(NSString*)formName field:(NSString*)fieldName {
   NSString* selectPreviousElementJS = [NSString
       stringWithFormat:@"__gCrWeb.suggestion.selectPreviousElement(%@, %@)",
                        JSONEscape(formName), JSONEscape(fieldName)];
-  [self evaluate:selectPreviousElementJS stringResultHandler:nil];
+  [self executeJavaScript:selectPreviousElementJS completionHandler:nil];
 }
 
 - (void)fetchPreviousAndNextElementsPresenceWithCompletionHandler:
         (void (^)(BOOL, BOOL))completionHandler {
   [self fetchPreviousAndNextElementsPresenceForForm:@""
                                               field:@""
                                   completionHandler:completionHandler];
 }
 
 - (void)fetchPreviousAndNextElementsPresenceForForm:(NSString*)formName
                                               field:(NSString*)fieldName
                                   completionHandler:
                                       (void (^)(BOOL, BOOL))completionHandler {
   DCHECK(completionHandler);
   DCHECK([self hasBeenInjected]);
-  id stringResultHandler = ^(NSString* result, NSError* error) {
+  NSString* escapedFormName = JSONEscape(formName);
+  NSString* escapedFieldName = JSONEscape(fieldName);
+  NSString* JS = [NSString
+      stringWithFormat:@"[__gCrWeb.suggestion.hasPreviousElement(%@, %@),"
+                       @"__gCrWeb.suggestion.hasNextElement(%@, %@)]"
+                       @".toString()",
+                       escapedFormName, escapedFieldName, escapedFormName,
+                       escapedFieldName];
+  [self executeJavaScript:JS completionHandler:^(id result, NSError* error) {
     // The result maybe an empty string here due to 2 reasons:
     // 1) When there is an exception running the JS
     // 2) There is a race when the page is changing due to which
     // JSSuggestionManager has not yet injected __gCrWeb.suggestion object
     // Handle this case gracefully.
     // TODO(shreyasv): Figure out / narrow down further why this occurs.
     // crbug.com/432217.
     // If a page has overridden Array.toString, the string returned may not
     // contain a ",", hence this is a defensive measure to early return.
     NSArray* components = [result componentsSeparatedByString:@","];

[Justin Donnelly, 2016/08/17 14:29:18]

Dumb Obj-C question: you don't need to cast result to NSString before calling
componentsSeparatedByString: on it?

[Eugene But (OOO till 7-30), 2016/08/17 15:33:27]

I think this code is fine as it is. .toString() should either return string or
throw exception. If former then |result| is already a string. If latter then
|result| will be nil and this code will fail gracefully as well.

     if (components.count != 2) {
       completionHandler(NO, NO);
       return;
     }
 
     DCHECK([components[0] isEqualToString:@"true"] ||
            [components[0] isEqualToString:@"false"]);
     BOOL hasPreviousElement = [components[0] isEqualToString:@"true"];
     DCHECK([components[1] isEqualToString:@"true"] ||
            [components[1] isEqualToString:@"false"]);
     BOOL hasNextElement = [components[1] isEqualToString:@"true"];
     completionHandler(hasPreviousElement, hasNextElement);
-  };
-  NSString* escapedFormName = JSONEscape(formName);
-  NSString* escapedFieldName = JSONEscape(fieldName);
-  NSString* js = [NSString
-      stringWithFormat:@"[__gCrWeb.suggestion.hasPreviousElement(%@, %@),"
-                       @"__gCrWeb.suggestion.hasNextElement(%@, %@)]"
-                       @".toString()",
-                       escapedFormName, escapedFieldName, escapedFormName,
-                       escapedFieldName];
-  [self evaluate:js stringResultHandler:stringResultHandler];
+  }];
 }
 
 - (void)closeKeyboard {
   [self executeJavaScript:@"document.activeElement.blur()"
         completionHandler:nil];
 }
 
 @end