Fix grokdump.py wrt KNOWN_MAPS format.

R=delphick@chromium.org

Change-Id: Iad00b090d1576a4a556e0971bbea3003a3aedb3f
Reviewed-on: https://chromium-review.googlesource.com/982631Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52265}

tools/grokdump.py

@@ -2063,7 +2063,8 @@ class InspectionPadawan(object):
   def SenseMap(self, tagged_address):
     if self.IsInKnownMapSpace(tagged_address):
       offset = self.GetPageOffset(tagged_address)
-      known_map_info = KNOWN_MAPS.get(offset)
+      lookup_key = ("MAP_SPACE", offset)
+      known_map_info = KNOWN_MAPS.get(lookup_key)
       if known_map_info:
         known_map_type, known_map_name = known_map_info
         return KnownMap(self, known_map_name, known_map_type)