Add FailureValue and wire it through PageTestResults.

tools/perf/measurements/skpicture_printer_unittest.py

 # Copyright 2014 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.
 
 import shutil
 import tempfile
 
 from measurements import skpicture_printer
 from telemetry.page import page_measurement_unittest_base
 from telemetry.unittest import options_for_unittests
 from telemetry.unittest import test
+from telemetry.value import failure
 
 
 class SkpicturePrinterUnitTest(
       page_measurement_unittest_base.PageMeasurementUnitTestBase):
   def setUp(self):
     self._options = options_for_unittests.GetCopy()
     self._options.skp_outdir = tempfile.mkdtemp('_skp_test')
 
   def tearDown(self):
     shutil.rmtree(self._options.skp_outdir)
 
   @test.Disabled('android')
   def testSkpicturePrinter(self):
     ps = self.CreatePageSetFromFileInUnittestDataDir('blank.html')
     measurement = skpicture_printer.SkpicturePrinter()
     results = self.RunMeasurement(measurement, ps, options=self._options)
 
     # Picture printing is not supported on all platforms.
     if results.failures:
-      assert 'not supported' in results.failures[0][1]
+      assert 'not supported' in failure.GetStringFromExcInfo(
+          results.failures[0].exc_info)
       return
 
     saved_picture_count = results.FindAllPageSpecificValuesNamed(
         'saved_picture_count')
     self.assertEquals(len(saved_picture_count), 1)
     self.assertGreater(saved_picture_count[0].GetRepresentativeNumber(), 0)