Add FilePath to base namespace.

chrome/browser/chromeos/drive/drive_system_service.h

Index: chrome/browser/chromeos/drive/drive_system_service.h
diff --git a/chrome/browser/chromeos/drive/drive_system_service.h b/chrome/browser/chromeos/drive/drive_system_service.h
index d36cc289e93aa14fa8f26b748b8668a77f1e03fd..bbd0c8a20c20892dd519cf7fb3b909a981157404 100644
--- a/chrome/browser/chromeos/drive/drive_system_service.h
+++ b/chrome/browser/chromeos/drive/drive_system_service.h
@@ -17,7 +17,9 @@
 #include "chrome/browser/profiles/profile_keyed_service_factory.h"
 #include "sync/notifier/invalidation_handler.h"
 
+namespace base {
 class FilePath;
+}
 
 namespace google_apis {
 class DriveServiceInterface;
@@ -50,7 +52,7 @@ class DriveSystemService : public ProfileKeyedService,
   // Pass NULL or the empty value when not interested.
   DriveSystemService(Profile* profile,
                      google_apis::DriveServiceInterface* test_drive_service,
-                     const FilePath& test_cache_root,
+                     const base::FilePath& test_cache_root,
                      DriveFileSystemInterface* test_file_system);
   virtual ~DriveSystemService();