faft: Unify ModeSwitcher APIs to support sync_before_boot

This change refines the time of calling sync_before_boot() to the entries
of main APIs. It helps some later refactoring.

BUG=chrome-os-partner:16231
TEST=Ran the affected tests, e.g. firmware_TPMExtend, firmware_EventLog,
firmware_RecoveryButton, firmware_DevMode, etc.

Change-Id: I0705bf7c01ae2e8bd94e64b1f6b0ab84ab36f790
Reviewed-on: https://chromium-review.googlesource.com/270763
Trybot-Ready: Tom Tam <waihong@google.com>
Tested-by: Tom Tam <waihong@google.com>
Reviewed-by: Yusuf Mohsinally <mohsinally@chromium.org>
Commit-Queue: Tom Tam <waihong@google.com>
diff --git a/server/cros/faft/firmware_test.py b/server/cros/faft/firmware_test.py
index db9d2ee..365021ab 100644
--- a/server/cros/faft/firmware_test.py
+++ b/server/cros/faft/firmware_test.py
@@ -316,7 +316,8 @@
         @raise TestError: if failed to boot the USB image.
         """
         logging.info('Try boot into USB image...')
-        self.switcher.reboot_to_mode(to_mode='rec', wait_for_dut_up=False)
+        self.switcher.reboot_to_mode(to_mode='rec', sync_before_boot=False,
+                                     wait_for_dut_up=False)
         self.servo.switch_usbkey('host')
         self.wait_fw_screen_and_plug_usb()
         try:
@@ -1014,7 +1015,7 @@
         is_dev = self.checkers.crossystem_checker({'devsw_boot': '1'})
         if not is_dev:
             self.switcher.reboot_to_mode(to_mode='dev', wait_for_dut_up=False)
-        self.switcher.reboot_to_mode(to_mode='rec')
+        self.switcher.reboot_to_mode(to_mode='rec', sync_before_boot=False)
         self.wait_fw_screen_and_plug_usb()
         time.sleep(self.faft_config.install_shim_done)
         self.switcher.mode_aware_reboot()