Implement break signal for serial api.

`Break` is somewhat related to control signaling and holds tx line low for n milliseconds.
Adding platform specific implementation.

BUG=461169
TEST=Manual with attached application on crbug.com/461169

Review URL: https://codereview.chromium.org/1128943005

Cr-Commit-Position: refs/heads/master@{#334111}

1 files changed, 8 insertions, 0 deletions

diff --git a/device/serial/test_serial_io_handler.cc b/device/serial/test_serial_io_handler.cc
index 9713c07..0dcb048 100644
--- a/device/serial/test_serial_io_handler.cc
+++ b/device/serial/test_serial_io_handler.cc
@@ -101,6 +101,14 @@ bool TestSerialIoHandler::SetControlSignals(
   return true;
 }
 
+bool TestSerialIoHandler::SetBreak() {
+  return true;
+}
+
+bool TestSerialIoHandler::ClearBreak() {
+  return true;
+}
+
 TestSerialIoHandler::~TestSerialIoHandler() {
 }