Don't use command line flags for enabling the internal pdf plugin. Instead, ...

chrome/common/pref_names.h

 // Copyright (c) 2010 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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 
 #include "build/build_config.h"
@@ skipping 113 matching lines @@
 extern const wchar_t kCurrentThemePackFilename[];
 extern const wchar_t kCurrentThemeID[];
 extern const wchar_t kCurrentThemeImages[];
 extern const wchar_t kCurrentThemeColors[];
 extern const wchar_t kCurrentThemeTints[];
 extern const wchar_t kCurrentThemeDisplayProperties[];
 extern const wchar_t kExtensionsUIDeveloperMode[];
 extern const wchar_t kExtensionToolbarSize[];
 extern const wchar_t kPluginsLastInternalDirectory[];
 extern const wchar_t kPluginsPluginsList[];
+extern const wchar_t kPluginsEnabledInternalPDF[];
 extern const wchar_t kCheckDefaultBrowser[];
 #if defined(OS_MACOSX)
 extern const wchar_t kShowUpdatePromotionInfoBar[];
 #endif
 extern const wchar_t kUseCustomChromeFrame[];
 extern const wchar_t kShowOmniboxSearchHint[];
 extern const wchar_t kNTPPromoLineRemaining[];
 extern const wchar_t kNTPPromoImageRemaining[];
 extern const wchar_t kDesktopNotificationAllowedOrigins[];
 extern const wchar_t kDesktopNotificationDeniedOrigins[];
@@ skipping 151 matching lines @@
 extern const wchar_t kLoginDatabaseMigrated[];
 
 extern const wchar_t kCloudPrintServiceURL[];
 extern const wchar_t kCloudPrintProxyId[];
 extern const wchar_t kCloudPrintProxyName[];
 extern const wchar_t kCloudPrintAuthToken[];
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_