Windows perf bots: fixes android pylib initialization.

Following crrev.com/202558, android's pylib was initialized on platforms that didn't need.
Check for platform and also make it safer to use should there be problems with "which".

BUG=242960
R=tonyg@chromium.org

Review URL: https://codereview.chromium.org/15804004

git-svn-id: http://src.chromium.org/svn/trunk/src/build@202669 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/__init__.py

@@ -4,14 +4,16 @@
 
 import os
 import subprocess
+import sys
 
 
-if not os.environ.get('ANDROID_SDK_ROOT'):
+if sys.platform == 'linux2' and not os.environ.get('ANDROID_SDK_ROOT'):
   # If envsetup.sh hasn't been sourced and there's no adb in the path,
   # set it here.
+  try:
     with file(os.devnull, 'w') as devnull:
-    ret = subprocess.call(['which', 'adb'], stdout=devnull, stderr=devnull)
-    if ret:
+      subprocess.call(['adb', 'version'], stdout=devnull, stderr=devnull)
+  except OSError:
       print 'No adb found in $PATH, fallback to checked in binary.'
       os.environ['PATH'] += os.pathsep + os.path.abspath(os.path.join(
           os.path.dirname(__file__),