Add Value FromDict to Telemetry

tools/telemetry/telemetry/value/__init__.py

Index: tools/telemetry/telemetry/value/__init__.py
diff --git a/tools/telemetry/telemetry/value/__init__.py b/tools/telemetry/telemetry/value/__init__.py
index 816e7cfa051de18be91a4d7538b356fcbb1f1d71..bfebc53afa87abe8dc5f483a5b4d2cf93fc32f2d 100644
--- a/tools/telemetry/telemetry/value/__init__.py
+++ b/tools/telemetry/telemetry/value/__init__.py
@@ -1,4 +1,4 @@
-# Copyright 2013 The Chromium Authors. All rights reserved.
+# 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.
 """
@@ -20,6 +20,10 @@ Downstream consumers of test results typically want to group these runs
 together, then compute summary statistics across runs. Value provides the
 Merge* family of methods for this kind of aggregation.
 """
+import os
+
+from telemetry.core import discover
+from telemetry.core import util
 
 # When combining a pair of Values togehter, it is sometimes ambiguous whether
 # the values should be concatenated, or one should be picked as representative.
@@ -161,22 +165,20 @@ class Value(object):
     """
     raise NotImplementedError()
 
-  @classmethod
-  def GetJSONTypeName(cls):
+  @staticmethod
+  def GetJSONTypeName():
     """Gets the typename for serialization to JSON using AsDict."""
     raise NotImplementedError()
 
   def AsDict(self):
-    """Gets a representation of this value as a dict for eventual
-    serialization to JSON.
-    """
+    """Pre-serializes a value to a dict for output as JSON."""
     return self._AsDictImpl()
 
   def _AsDictImpl(self):
     d = {
       'name': self.name,
       'type': self.GetJSONTypeName(),
-      'unit': self.units,
+      'units': self.units,
     }
 
     if self.description:
@@ -195,6 +197,81 @@ class Value(object):
     return dict([(k, v) for (k, v) in full_dict.iteritems()
                   if k not in base_dict_keys])
 
+  @staticmethod
+  def FromDict(value_dict, page_dict):
+    """Produces a value from a value dict and a page dict.
+
+    Value dicts are produced by serialization to JSON, and must be accompanied
+    by a dict mapping page IDs to pages, also produced by serialization, in
+    order to be completely deserialized. If deserializing multiple values, use
+    ListOfValuesFromListOfDicts instead.
+
+    value_dict: a dictionary produced by AsDict() on a value subclass.
+    page_dict: a dictionary mapping IDs to page objects.
+    """
+    return Value.ListOfValuesFromListOfDicts([value_dict], page_dict)[0]
+
+  @staticmethod
+  def ListOfValuesFromListOfDicts(value_dicts, page_dict):
+    """Takes a list of value dicts to values.
+
+    Given a list of value dicts produced by AsDict, this method
+    deserializes the dicts given a dict mapping page IDs to pages.
+    This method performs memoization for deserializing a list of values
+    efficiently, where FromDict is meant to handle one-offs.
+
+    values: a list of value dicts produced by AsDict() on a value subclass.
+    page_dict: a dictionary mapping IDs to page objects.
+    """
+    value_dir = os.path.dirname(__file__)
+    value_classes = discover.DiscoverClasses(
+        value_dir, util.GetTelemetryDir(),
+        Value, index_by_class_name=True)
+
+    value_json_types = dict((value_classes[x].GetJSONTypeName(), x) for x in
+        value_classes)
+
+    values = []
+    for value_dict in value_dicts:
+      value_class = value_classes[value_json_types[value_dict['type']]]
+      assert 'FromDict' in value_class.__dict__, \
+             'Subclass doesn\'t override FromDict'
+      values.append(value_class.FromDict(value_dict, page_dict))
+
+    return values
+
+  @staticmethod
+  def GetConstructorKwArgs(value_dict, page_dict):
+    """Produces constructor arguments from a value dict and a page dict.
+
+    Takes a dict parsed from JSON and an index of pages and recovers the
+    keyword arguments to be passed to the constructor for deserializing the
+    dict.
+
+    value_dict: a dictionary produced by AsDict() on a value subclass.
+    page_dict: a dictionary mapping IDs to page objects.
+    """
+    d = {
+      'name': value_dict['name'],
+      'units': value_dict['units']
+    }
+
+    description = value_dict.get('description', None)
+    if description:
+      d['description'] = description
+    else:
+      d['description'] = None
+
+    page_id = value_dict.get('page_id', None)
+    if page_id:
+      d['page'] = page_dict[int(page_id)]
+    else:
+      d['page'] = None
+
+    d['important'] = False
+
+    return d
+
 def ValueNameFromTraceAndChartName(trace_name, chart_name=None):
   """Mangles a trace name plus optional chart name into a standard string.