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

Python 2.7.x includes pySerial version 2.5 as a distribution package. This conflicts with
our repository version of pySerial i.e. 2.7. The submodule serial.tools.* was included in
pySerial after 2.6 as per [1].

The utility function util.AddDirToPythonPath(...) appends the path at the end of the path
list. Due to this, the python interpreter picks up the pySerial library from system include
path at /usr/lib/python2.7/dist-packages/serial. This CL modifies AddDirToPythonPath(...) API to always prepend the path.

[1] http://pyserial.sourceforge.net/pyserial_api.html#module-serial.tools.list_ports

NOTRY=true

Review URL: https://codereview.chromium.org/321773002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276531 0039d316-1c4b-4281-b951-d872f2087c98

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

@@ -44,6 +44,8 @@ class 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

tools/telemetry/telemetry/core/util.py

@@ -39,7 +39,7 @@ def GetChromiumSrcDir():
 def AddDirToPythonPath(*path_parts):
   path = os.path.abspath(os.path.join(*path_parts))
   if os.path.isdir(path) and path not in sys.path:
-    sys.path.append(path)
+    sys.path.insert(0, path)
 
 _counter = [0]
 def _GetUniqueModuleName():