Report all swarming and isolate fatal errors in a consistent way.

utils/tools.py

Index: utils/tools.py
diff --git a/utils/tools.py b/utils/tools.py
index eecf709641bc8497a3d8e57480a65b3a8071d029..1c793a68f92928ae642e27673c8268cf587ab376 100644
--- a/utils/tools.py
+++ b/utils/tools.py
@@ -10,6 +10,7 @@ import optparse
 import os
 import sys
 import time
+import traceback
 
 
 class OptionParserWithLogging(optparse.OptionParser):
@@ -112,3 +113,21 @@ def fix_python_path(cmd):
   elif out[0].endswith('.py'):
     out.insert(0, sys.executable)
   return out
+
+
+def report_error(message, include_traceback=False):
+  """Prints a error to stderr, wrapping it into header and footer.
+
+  That way errors can be reliably extracted from logs. It's indented to be used
+  only for non recoverable unexpected errors. Is should NOT be used for input
+  validation, command line argument errors, etc.
+
+  Arguments:
+    message: error message string, possibly multiple lines.
+    include_traceback: True to append traceback of current exception.
+  """
+  print >> sys.stderr, '[------ Swarming Error ------]'
+  print >> sys.stderr, message
+  if include_traceback:
+    print >> sys.stderr, traceback.format_exc(),
+  print >> sys.stderr, '[----------------------------]'