Implement break signal for serial api.

device/serial/serial_io_handler.h

Index: device/serial/serial_io_handler.h
diff --git a/device/serial/serial_io_handler.h b/device/serial/serial_io_handler.h
index 1b2a8c49d4ac47fd0dca17174c6e9d50da4d23b6..bd8255e03b18edb824687f3cd7cabbabab55398d 100644
--- a/device/serial/serial_io_handler.h
+++ b/device/serial/serial_io_handler.h
@@ -83,6 +83,14 @@ class SerialIoHandler : public base::NonThreadSafe,
   // successfully retrieved.
   virtual serial::ConnectionInfoPtr GetPortInfo() const = 0;
 
+  // Initiates a BREAK signal. Places the transmission line in a break state
+  // until the |ClearBreak| is called.
+  virtual bool SetBreak() = 0;
+
+  // Terminates the BREAK signal. Places the transmission line in a nonbreak
+  // state.
+  virtual bool ClearBreak() = 0;
+
  protected:
   explicit SerialIoHandler(
       scoped_refptr<base::SingleThreadTaskRunner> file_thread_task_runner,