Move WriteFile and WriteFileDescriptor from file_util to base namespace.

remoting/host/json_host_config_unittest.cc

Index: remoting/host/json_host_config_unittest.cc
diff --git a/remoting/host/json_host_config_unittest.cc b/remoting/host/json_host_config_unittest.cc
index 76f2912f49bcbe66002c43816e1bf502814de894..a3fdf96d43f4d7df05442f97324bddd09c5c0eca 100644
--- a/remoting/host/json_host_config_unittest.cc
+++ b/remoting/host/json_host_config_unittest.cc
@@ -25,7 +25,7 @@ const char* kTestConfig =
 class JsonHostConfigTest : public testing::Test {
  protected:
   static void WriteTestFile(const base::FilePath& filename) {
-    file_util::WriteFile(filename, kTestConfig, std::strlen(kTestConfig));
+    base::WriteFile(filename, kTestConfig, std::strlen(kTestConfig));
   }
 
   // The temporary directory used to contain the test operations.