Add FailureValue and wire it through PageTestResults.

tools/telemetry/telemetry/value/failure.py

Index: tools/telemetry/telemetry/value/failure.py
diff --git a/tools/telemetry/telemetry/value/failure.py b/tools/telemetry/telemetry/value/failure.py
new file mode 100644
index 0000000000000000000000000000000000000000..08e2b9e8888cd7273cea1654ee8476129dabca96
--- /dev/null
+++ b/tools/telemetry/telemetry/value/failure.py
@@ -0,0 +1,83 @@
+# 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 sys
+import traceback
+
+from telemetry import value as value_module
+
+class FailureValue(value_module.Value):
+
+  def __init__(self, page, exc_info):
+    """A value representing a failure when running the page.
+
+    Args:
+      page: The page where this failure occurs.
+      exc_info: The exception info (sys.exc_info()) corresponding to
+          this failure.
+    """
+    exc_type = exc_info[0].__name__
+    super(FailureValue, self).__init__(page, exc_type, '', True)
+    self._exc_info = exc_info
+
+  @classmethod
+  def FromMessage(cls, page, message):
+    """Creates a failure value for a given string message.
+
+    Args:
+      page: The page where this failure occurs.
+      message: A string message describing the failure.
+    """
+    try:
+      raise Exception(message)
+    except Exception:
+      return FailureValue(page, sys.exc_info())
+
+  def __repr__(self):
+    if self.page:
+      page_name = self.page.url
+    else:
+      page_name = None
+    return 'FailureValue(%s, %s)' % (
+        page_name, GetStringFromExcInfo(self._exc_info))
+
+  @property
+  def exc_info(self):
+    return self._exc_info
+
+  def GetBuildbotDataType(self, output_context):
+    return None
+
+  def GetBuildbotValue(self):
+    return None
+
+  def GetBuildbotMeasurementAndTraceNameForPerPageResult(self):
+    return None
+
+  def GetRepresentativeNumber(self):
+    return None
+
+  def GetRepresentativeString(self):
+    return None
+
+  @classmethod
+  def GetJSONTypeName(cls):
+    return 'failure'
+
+  def AsDict(self):
+    d = super(FailureValue, self).AsDict()
+    d['value'] = GetStringFromExcInfo(self.exc_info)
+    return d
+
+  @classmethod
+  def MergeLikeValuesFromSamePage(cls, values):
+    assert False, 'Should not be called.'
+
+  @classmethod
+  def MergeLikeValuesFromDifferentPages(cls, values,
+                                        group_by_name_suffix=False):
+    assert False, 'Should not be called.'
+
+def GetStringFromExcInfo(exc_info):
+  return ''.join(traceback.format_exception(*exc_info))