gcapi/mac: Prevent "unknown binary" stderr output from sudo

chrome/installer/gcapi_mac/gcapi.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 "chrome/installer/gcapi_mac/gcapi.h"
 
 #import <Cocoa/Cocoa.h>
 #include <grp.h>
 #include <pwd.h>
 #include <sys/stat.h>
@@ skipping 90 matching lines @@
   // Don't use Objective-C 2 loop syntax, in case an installer runs on 10.4.
   NSMutableArray* keystone_paths =
       [NSMutableArray arrayWithObject:kSystemKsadminPath];
   if (kind == kUserTicket) {
     [keystone_paths insertObject:AdjustHomedir(kUserKsadminPath, user->pw_dir)
                         atIndex:0];
   }
   NSEnumerator* e = [keystone_paths objectEnumerator];
   id ks_path;
   while ((ks_path = [e nextObject])) {
+    if (![[NSFileManager defaultManager] fileExistsAtPath:ks_path])
+      continue;
+
     NSTask* task = nil;
     NSString* string = nil;
     bool ksadmin_ran_successfully = false;
 
     @try {
       task = [[NSTask alloc] init];
       [task setLaunchPath:ks_path];
 
       NSArray* arguments = @[
           kind == kUserTicket ? @"--user-store" : @"--system-store",
@@ skipping 237 matching lines @@
   return 1;
 }
 
 int LaunchGoogleChrome() {
   @autoreleasepool {
     // NSWorkspace launches processes as the current console owner,
     // even when running with euid of 0.
     return [[NSWorkspace sharedWorkspace] launchApplication:kChromeInstallPath];
   }
 }