Fix BrowserAccessibilityManagerMac: set empty selected text range.

content/browser/accessibility/browser_accessibility_manager_mac.mm

 // Copyright (c) 2012 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.
 
 #include "content/browser/accessibility/browser_accessibility_manager_mac.h"
 
 #import "base/mac/mac_util.h"
 #import "base/mac/sdk_forward_declarations.h"
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 407 matching lines @@
   [user_info setObject:@(AXTextSelectionGranularityUnknown)
                 forKey:NSAccessibilityTextSelectionGranularity];
   [user_info setObject:@YES forKey:NSAccessibilityTextSelectionChangedFocus];
 
   int32_t focus_id = GetTreeData().sel_focus_object_id;
   BrowserAccessibility* focus_object = GetFromID(focus_id);
   if (focus_object) {
     focus_object = focus_object->GetClosestPlatformObject();
     auto native_focus_object = ToBrowserAccessibilityCocoa(focus_object);
     if (native_focus_object && [native_focus_object instanceActive]) {
-      [user_info setObject:[native_focus_object selectedTextMarkerRange]
-                    forKey:NSAccessibilitySelectedTextMarkerRangeAttribute];
       [user_info setObject:native_focus_object
                     forKey:NSAccessibilityTextChangeElement];
+
+      id selected_text = [native_focus_object selectedTextMarkerRange];
+      if (selected_text) {
+        [user_info setObject:selected_text
+                      forKey:NSAccessibilitySelectedTextMarkerRangeAttribute];
+      }
     }
   }
 
   return user_info;
 }
 
 NSDictionary*
 BrowserAccessibilityManagerMac::GetUserInfoForValueChangedNotification(
     const BrowserAccessibilityCocoa* native_node,
     const base::string16& deleted_text,
@@ skipping 19 matching lines @@
   }
 
   return @{
     NSAccessibilityTextStateChangeTypeKey : @(AXTextStateChangeTypeEdit),
     NSAccessibilityTextChangeValues : changes,
     NSAccessibilityTextChangeElement : native_node
   };
 }
 
 }  // namespace content