Use NSAccessibility constants instead their string values

Bug: 1060615

Change-Id: I7219f1b5f0c83c243bf6ccbd407b55ed93960b4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2098259Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749262}

content/browser/accessibility/browser_accessibility_cocoa.mm

@@ -3002,14 +3002,16 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
     return [NSValue valueWithRect:nsrect];
   }
 
-  if ([attribute isEqualToString:@"AXUIElementCountForSearchPredicate"]) {
+  if ([attribute isEqualToString:
+                   NSAccessibilityUIElementCountForSearchPredicateParameterizedAttribute]) {
     OneShotAccessibilityTreeSearch search(_owner);
     if (InitializeAccessibilityTreeSearch(&search, parameter))
       return [NSNumber numberWithInt:search.CountMatches()];
     return nil;
   }
 
-  if ([attribute isEqualToString:@"AXUIElementsForSearchPredicate"]) {
+  if ([attribute isEqualToString:
+                     NSAccessibilityUIElementsForSearchPredicateParameterizedAttribute]) {
     OneShotAccessibilityTreeSearch search(_owner);
     if (InitializeAccessibilityTreeSearch(&search, parameter)) {
       size_t count = search.CountMatches();