Mojo: Make the mojom bindings generator not exponential in the import depth.

We don't need to do deep copies -- shallow copies will do. However, for
structs and such, we need to carefully work around the shared_definition
nonsense.

R=jamesr@chromium.org
BUG=406156

Review URL: https://codereview.chromium.org/535333002

Cr-Commit-Position: refs/heads/master@{#293352}

mojo/public/tools/bindings/pylib/mojom/generate/data.py

@@ -134,7 +134,12 @@ def KindFromData(kinds, data, scope):
 def KindFromImport(original_kind, imported_from):
   """Used with 'import module' - clones the kind imported from the given
   module's namespace. Only used with Structs, Interfaces and Enums."""
-  kind = copy.deepcopy(original_kind)
+  kind = copy.copy(original_kind)
+  # |shared_definition| is used to store various properties (see
+  # |AddSharedProperty()| in module.py), including |imported_from|. We don't
+  # want the copy to share these with the original, so copy it if necessary.
+  if hasattr(original_kind, 'shared_definition'):
+    kind.shared_definition = copy.copy(original_kind.shared_definition)
   kind.imported_from = imported_from
   return kind
 
@@ -155,7 +160,9 @@ def ImportFromData(module, data):
   # Ditto for values.
   for value in import_module.values.itervalues():
     if value.imported_from is None:
-      value = copy.deepcopy(value)
+      # Values don't have shared definitions (since they're not nullable), so no
+      # need to do anything special.
+      value = copy.copy(value)
       value.imported_from = import_item
       module.values[value.GetSpec()] = value