Remove //chrome dependency from ExtensionPrefs

extensions/browser/test_extensions_browser_client.cc

 // Copyright 2014 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 "extensions/browser/test_extensions_browser_client.h"
 
 #include "content/public/browser/browser_context.h"
 #include "extensions/browser/app_sorting.h"
 #include "extensions/browser/extension_host_delegate.h"
 
@@ skipping 112 matching lines @@
 ExtensionSystemProvider*
 TestExtensionsBrowserClient::GetExtensionSystemFactory() {
   // Tests requiring an extension system should override this function.
   NOTREACHED();
   return NULL;
 }
 
 void TestExtensionsBrowserClient::RegisterExtensionFunctions(
     ExtensionFunctionRegistry* registry) const {}
 
+void TestExtensionsBrowserClient::AddExtensionPrefsObservers(
+    content::BrowserContext* context,
+    ExtensionPrefs* prefs) const {}
+
 }  // namespace extensions