[Findit] Fix KeyError when no failed targets are extracted.

appengine/findit/waterfall/test/try_job_util_test.py

 # Copyright 2015 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.
 
 from testing_utils import testing
 
 from model import wf_analysis_status
 from model.wf_analysis import WfAnalysis
 from model.wf_try_job import WfTryJob
 from waterfall import try_job_util
@@ skipping 366 matching lines @@
 
     try_job = WfTryJob.Get(master_name, builder_name, build_number)
 
     self.assertTrue(_MockRootPipeline.STARTED)
     self.assertIsNotNone(try_job)
 
   def testGetFailedTargetsFromSignals(self):
     self.assertEqual(
         try_job_util._GetFailedTargetsFromSignals({}, 'm', 'b'), [])
 
+    self.assertEqual(
+        try_job_util._GetFailedTargetsFromSignals({'compile': {}}, 'm', 'b'),
+        [])
+
     signals = {
         'compile': {
             'failed_targets': [
                 {'target': 'a.exe'},
                 {'source': 'b.cc',
                  'target': 'b.o'}]
         }
     }
 
     self.assertEqual(
         try_job_util._GetFailedTargetsFromSignals(signals, 'm', 'b'), ['a.exe'])
 
   def testUseObjectFilesAsFailedTargetIfStrictRegexUsed(self):
     def Mocked_EnableStrictRegexForCompileLinkFailures(*_):
       return True
     self.mock(waterfall_config, 'EnableStrictRegexForCompileLinkFailures',
               Mocked_EnableStrictRegexForCompileLinkFailures)
 
     signals = {
         'compile': {
             'failed_targets': [
                 {'source': 'b.cc', 'target': 'b.o'},
             ]
         }
     }
 
     self.assertEqual(
         try_job_util._GetFailedTargetsFromSignals(signals, 'm', 'b'), ['b.o'])