Handle multiple modifications to distribution metrics correctly.

infra_libs/ts_mon/common/metric_store.py

Index: infra_libs/ts_mon/common/metric_store.py
diff --git a/infra_libs/ts_mon/common/metric_store.py b/infra_libs/ts_mon/common/metric_store.py
index c40333f7ae519ca58ca5c08425b60ae07fb1c776..5bb6c30681c1637394f55809b2ac168d3913dd88 100644
--- a/infra_libs/ts_mon/common/metric_store.py
+++ b/infra_libs/ts_mon/common/metric_store.py
@@ -24,26 +24,6 @@ Modification = collections.namedtuple(
     'Modification', ['name', 'fields', 'mod_type', 'args'])
 
 
-def combine_modifications(old, new):
-  """Combines two modifications into one.
-
-  The returned modification will be the result as if the second modification had
-  been applied after the first.
-  """
-
-  if old is None or new.mod_type == 'set':
-    # A 'set' will override any previous value.
-    return new
-  elif new.mod_type == 'incr':
-    # For two 'incr's sum their delta args, for an 'incr' on top of a 'set' add
-    # the delta to the set value.
-    return Modification(
-        old.name, old.fields, old.mod_type,
-        (old.args[0] + new.args[0], old.args[1]))
-  else:
-    raise errors.UnknownModificationTypeError(new.mod_type)
-
-
 class MetricStore(object):
   """A place to store values for each metric.