Adds a pref and a policy to decide if PDFs should always be opened externally.

chrome/browser/plugins/plugin_prefs.h

Index: chrome/browser/plugins/plugin_prefs.h
diff --git a/chrome/browser/plugins/plugin_prefs.h b/chrome/browser/plugins/plugin_prefs.h
index 33fe31ae5bd1ae22256a25de6c1b3d6a97f40ded..05c8159d48fcc981a916a87b1de93e1901613705 100644
--- a/chrome/browser/plugins/plugin_prefs.h
+++ b/chrome/browser/plugins/plugin_prefs.h
@@ -13,6 +13,7 @@
 #include "base/macros.h"
 #include "base/synchronization/lock.h"
 #include "chrome/browser/plugins/plugin_finder.h"
+#include "chrome/common/chrome_content_client.h"
 #include "components/keyed_service/core/refcounted_keyed_service.h"
 #include "components/prefs/pref_change_registrar.h"
 #include "components/prefs/pref_service.h"
@@ -107,12 +108,18 @@ class PluginPrefs : public RefcountedKeyedService {
   void UpdatePatternsAndNotify(std::set<base::string16>* patterns,
                                const std::string& pref_name);
 
+  // Callback for changes to the AlwaysOpenPdfExternally policy.
+  void UpdatePdfPolicy(const std::string& pref_name);
+
   // Allows unit tests to directly set enforced plugin patterns.
-  void SetPolicyEnforcedPluginPatterns(
+  void SetPolicyEnforcedPluginPatternsForTests(
       const std::set<base::string16>& disabled_patterns,
       const std::set<base::string16>& disabled_exception_patterns,
       const std::set<base::string16>& enabled_patterns);
 
+  // Allows unit tests to directly set the AlwaysOpenPdfExternally pref.
+  void SetAlwaysOpenPdfExternallyForTests(bool always_open_pdf_externally);
+
   // Callback for after the plugin groups have been loaded.
   void EnablePluginGroupInternal(
       bool enabled,
@@ -147,6 +154,7 @@ class PluginPrefs : public RefcountedKeyedService {
   std::set<base::string16> policy_disabled_plugin_patterns_;
   std::set<base::string16> policy_disabled_plugin_exception_patterns_;
   std::set<base::string16> policy_enabled_plugin_patterns_;
+  bool always_open_pdf_externally_;
 
   // Weak pointer, owns us. Only used as a notification source.
   Profile* profile_;