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

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

Index: tools/telemetry/telemetry/core/chrome/cros_browser_finder.py
diff --git a/tools/telemetry/telemetry/core/chrome/cros_browser_finder.py b/tools/telemetry/telemetry/core/chrome/cros_browser_finder.py
index 15c50a5b462c15ac818777a81867c50b34b7cb5a..a5ea97070e5bece63260a24714b092405dc0a311 100644
--- a/tools/telemetry/telemetry/core/chrome/cros_browser_finder.py
+++ b/tools/telemetry/telemetry/core/chrome/cros_browser_finder.py
@@ -44,6 +44,13 @@ class PossibleCrOSBrowser(possible_browser.PossibleBrowser):
       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():