Enable Clang warnings in .cc files for Linux+[Aura/ChromeOS]

chromeos/cryptohome/cryptohome_library.cc

Index: chromeos/cryptohome/cryptohome_library.cc
diff --git a/chromeos/cryptohome/cryptohome_library.cc b/chromeos/cryptohome/cryptohome_library.cc
index 9529836538636edd821bd8661f91fcf76777e717..f717e1eeb4068ca7218eef2ef4c8653b067ade11 100644
--- a/chromeos/cryptohome/cryptohome_library.cc
+++ b/chromeos/cryptohome/cryptohome_library.cc
@@ -290,12 +290,12 @@ class CryptohomeLibraryStubImpl : public CryptohomeLibrary {
     return kStubSystemSalt;
   }
 
-  virtual std::string EncryptWithSystemSalt(const std::string& token) {
+  virtual std::string EncryptWithSystemSalt(const std::string& token) OVERRIDE {
     return token;
   }
 
   virtual std::string DecryptWithSystemSalt(
-      const std::string& encrypted_token_hex) {
+      const std::string& encrypted_token_hex) OVERRIDE {
     return encrypted_token_hex;
   }