[PowerProfiler] Make sure correct version of pySerial is imported with monsoon profiler.

tools/telemetry/telemetry/core/platform/profiler/monsoon.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Interface for a USB-connected Monsoon power meter.
 
 http://msoon.com/LabEquipment/PowerMonitor/
 Currently Unix-only. Relies on fcntl, /dev, and /tmp.
 """
 
@@ skipping 26 matching lines @@
   """
 
   def __init__(self, device=None, serialno=None, wait=True):
     """Establish a connection to a Monsoon.
 
     By default, opens the first available port, waiting if none are ready.
     A particular port can be specified with 'device', or a particular Monsoon
     can be specified with 'serialno' (using the number printed on its back).
     With wait=False, IOError is thrown if a device is not immediately available.
     """
+    assert float(serial.VERSION) >= 2.7, \
+     'Monsoon requires pyserial v2.7 or later. You have %s' % serial.VERSION
 
     self._coarse_ref = self._fine_ref = self._coarse_zero = self._fine_zero = 0
     self._coarse_scale = self._fine_scale = 0
     self._last_seq = 0
     self._voltage_multiplier = None
 
     if device:
       self.ser = serial.Serial(device, timeout=1)
       return
 
@@ skipping 219 matching lines @@
         logging.error('exception from serial port')
         return None
       elif len(ready_r) > 0:
         flushed += 1
         self.ser.read(1)  # This may cause underlying buffering.
         self.ser.flush()  # Flush the underlying buffer too.
       else:
         break
     if flushed > 0:
       logging.debug('dropped >%d bytes', flushed)