Add more consitent exception generation and handling

tools/isolate/trace_test_cases.py

 #!/usr/bin/env python
 # 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.
 
 """A manual version of trace_inputs.py that is specialized in tracing each
 google-test test case individually.
 
 This is mainly written to work around bugs in strace w.r.t. browser_tests.
 """
@@ skipping 39 matching lines @@
       start = time.time()
       returncode, output = trace_inputs.trace(
           logname, cmd, os.path.join(root_dir, cwd_dir), api, True)
       if returncode and i < 5:
         print '\nFailed while running: %s' % ' '.join(cmd)
         continue
       duration = time.time() - start
       try:
         results, simplified = trace_inputs.load_trace(logname, root_dir, api)
         break
-      except Exception:
-        print '\nFailed loading the trace for: %s' % ' '.join(cmd)
+      except trace_inputs.TracingFailure, e:
+        print >> sys.stderr, '\nTracing failed for: %s' % ' '.join(cmd)
+        print >> sys.stderr, str(e)
     if simplified:
       variables = trace_inputs.generate_dict(simplified, cwd_dir, product_dir)
     else:
       variables = {}
     return {
       'case': test_case,
       'duration': duration,
       'output': output,
       'processes': processes,
       'result': returncode,
@@ skipping 137 matching lines @@
       options.cwd,
       options.product_dir,
       options.leak,
       options.skip,
       options.jobs,
       options.timeout)
 
 
 if __name__ == '__main__':
   sys.exit(main())