Add FailureValue and wire it through PageTestResults.

tools/perf/measurements/skpicture_printer_unittest.py

Index: tools/perf/measurements/skpicture_printer_unittest.py
diff --git a/tools/perf/measurements/skpicture_printer_unittest.py b/tools/perf/measurements/skpicture_printer_unittest.py
index e7871db626036d8a1721857fb50798aa483a2def..7c35992bcb282bd18fb4fd93576d1bbb4519d306 100644
--- a/tools/perf/measurements/skpicture_printer_unittest.py
+++ b/tools/perf/measurements/skpicture_printer_unittest.py
@@ -9,6 +9,7 @@ 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(
@@ -28,7 +29,8 @@ class SkpicturePrinterUnitTest(
 
     # 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(