ppapi: Use stl utilities from the base namespace

ppapi/proxy/file_system_resource.cc

Index: ppapi/proxy/file_system_resource.cc
diff --git a/ppapi/proxy/file_system_resource.cc b/ppapi/proxy/file_system_resource.cc
index 0be0ea52e5e30504ec32ad121dcca9bdb82e6656..37b2cc7275c4629de598ebf80425f5d145633d60 100644
--- a/ppapi/proxy/file_system_resource.cc
+++ b/ppapi/proxy/file_system_resource.cc
@@ -95,12 +95,12 @@ PP_FileSystemType FileSystemResource::GetType() {
 }
 
 void FileSystemResource::OpenQuotaFile(PP_Resource file_io) {
-  DCHECK(!ContainsKey(files_, file_io));
+  DCHECK(!base::ContainsKey(files_, file_io));
   files_.insert(file_io);
 }
 
 void FileSystemResource::CloseQuotaFile(PP_Resource file_io) {
-  DCHECK(ContainsKey(files_, file_io));
+  DCHECK(base::ContainsKey(files_, file_io));
   files_.erase(file_io);
 }