Fail gracefully when starting Chrome with an invalid kProfileDirectory.

chrome/browser/profiles/profiles_state.cc

 // 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.
 
 #include "chrome/browser/profiles/profiles_state.h"
 
 #include "base/files/file_path.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 175 matching lines @@
   ProfileManager* profile_manager = g_browser_process->profile_manager();
 
   const base::FilePath& active_profile_path =
       profile_manager->GetLastUsedProfileDir(profile_manager->user_data_dir());
   const base::FilePath& guest_path = ProfileManager::GetGuestProfilePath();
   if (active_profile_path == guest_path)
     return true;
 
   const ProfileInfoCache& cache = profile_manager->GetProfileInfoCache();
   size_t index = cache.GetIndexOfProfileWithPath(active_profile_path);
-  if (!cache.ProfileIsSigninRequiredAtIndex(index))
+  if (index == std::string::npos ||
+      !cache.ProfileIsSigninRequiredAtIndex(index)) {
     return false;
+  }
 
   PrefService* local_state = g_browser_process->local_state();
   DCHECK(local_state);
   local_state->SetString(
       prefs::kProfileLastUsed,
       guest_path.BaseName().MaybeAsASCII());
   return true;
 }
 
 }  // namespace profiles