Add Value FromDict to Telemetry

tools/telemetry/telemetry/value/string.py

Index: tools/telemetry/telemetry/value/string.py
diff --git a/tools/telemetry/telemetry/value/string.py b/tools/telemetry/telemetry/value/string.py
index a62832218edb017bf5ca7860707c41ea43233b8f..a36625d406e6a37234352464d1dca1ae8fa41e93 100644
--- a/tools/telemetry/telemetry/value/string.py
+++ b/tools/telemetry/telemetry/value/string.py
@@ -47,8 +47,8 @@ class StringValue(value_module.Value):
   def GetRepresentativeString(self):
     return str(self.value)
 
-  @classmethod
-  def GetJSONTypeName(cls):
+  @staticmethod
+  def GetJSONTypeName():
     return 'string'
 
   def AsDict(self):
@@ -56,6 +56,13 @@ class StringValue(value_module.Value):
     d['value'] = self.value
     return d
 
+  @staticmethod
+  def FromDict(value_dict, page_dict):
+    kwargs = value_module.Value.GetConstructorKwArgs(value_dict, page_dict)
+    kwargs['value'] = value_dict['value']
+
+    return StringValue(**kwargs)
+
   @classmethod
   def MergeLikeValuesFromSamePage(cls, values):
     assert len(values) > 0