Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/extensions/extension_prefs_unittest.h

Index: chrome/browser/extensions/extension_prefs_unittest.h
diff --git a/chrome/browser/extensions/extension_prefs_unittest.h b/chrome/browser/extensions/extension_prefs_unittest.h
index f96ffb6ca4d209e43fe50e058cb6e07af8af5f8f..c199d198cb52ca0ef3692f7e3f40ff6a0cd867b3 100644
--- a/chrome/browser/extensions/extension_prefs_unittest.h
+++ b/chrome/browser/extensions/extension_prefs_unittest.h
@@ -10,6 +10,8 @@
 #include "content/public/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+class PrefRegistrySyncable;
+
 namespace base {
 class Value;
 }
@@ -33,7 +35,7 @@ class ExtensionPrefsTest : public testing::Test {
   virtual void Verify() = 0;
 
   // This function is called to Register preference default values.
-  virtual void RegisterPreferences();
+  virtual void RegisterPreferences(PrefRegistrySyncable* registry);
 
   virtual void SetUp() OVERRIDE;
 
@@ -56,7 +58,7 @@ class ExtensionPrefsPrepopulatedTest : public ExtensionPrefsTest {
   ExtensionPrefsPrepopulatedTest();
   virtual ~ExtensionPrefsPrepopulatedTest();
 
-  virtual void RegisterPreferences() OVERRIDE;
+  virtual void RegisterPreferences(PrefRegistrySyncable* registry) OVERRIDE;
 
   void InstallExtControlledPref(Extension* ext,
                                 const std::string& key,