Remove DISALLOW_ macro from libcef_dll/ (see issue #3234)

Also perform related C++ cleanup:
- Use =default instead of {} for default implementations of
  constructors/destructors.
- Replace typedef with using.

libcef_dll/base/cef_logging.cc

@@ -191,7 +191,7 @@ LogMessage::~LogMessage() {
 // This has already been defined in the header, but defining it again as DWORD
 // ensures that the type used in the header is equivalent to DWORD. If not,
 // the redefinition is a compile error.
-typedef DWORD SystemErrorCode;
+using SystemErrorCode = DWORD;
 #endif
 
 SystemErrorCode GetLastSystemErrorCode() {