[Telemetry] Default to most recent local build if --browser is omitted.

tools/telemetry/telemetry/core/chrome/cros_browser_finder.py

 # Copyright (c) 2012 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.
 """Finds CrOS browsers that can be controlled by telemetry."""
 
 import logging
 
 from telemetry.core import browser
 from telemetry.core import possible_browser
 from telemetry.core import profile_types
@@ skipping 26 matching lines @@
     b = browser.Browser(backend,
                         cros_platform_backend.CrosPlatformBackend(self._cri))
     backend.SetBrowser(b)
     return b
 
   def SupportsOptions(self, options):
     if (len(options.extensions_to_load) != 0) and self._is_guest:
       return False
     return True
 
+def SelectDefaultBrowser(possible_browsers):
+  if cros_interface.IsRunningOnCrosDevice():
+    for b in possible_browsers:
+      if b.browser_type == 'system':
+        return b
+  return None
+
 def FindAllAvailableBrowsers(options):
   """Finds all available chromeos browsers, locally and remotely."""
   if cros_interface.IsRunningOnCrosDevice():
     return [PossibleCrOSBrowser('system', options,
                                 cros_interface.CrOSInterface(),
                                 is_guest=False),
             PossibleCrOSBrowser('system-guest', options,
                                 cros_interface.CrOSInterface(),
                                 is_guest=True)]
 
@@ skipping 33 matching lines @@
       logging.warn('P.S. Please, tell your manager how INANE this is.')
 
     from telemetry.core import browser_finder
     raise browser_finder.BrowserFinderException(str(ex))
 
   if not cri.FileExistsOnDevice('/opt/google/chrome/chrome'):
     logging.warn('Could not find a chrome on ' % cri.hostname)
 
   return [PossibleCrOSBrowser('cros-chrome', options, cri, is_guest=False),
           PossibleCrOSBrowser('cros-chrome-guest', options, cri, is_guest=True)]