Revert "Remove the restore_path() method"

This reverts commit 8151853 which was added while investigating
the slowdown caused by context's path copying. Turns out this change doesn't have a negative
impact on the performance but it has a positive one on the inference.

Author: PCManticore

astroid/context.py

@@ -7,7 +7,7 @@
 # For details: https://github.com/PyCQA/astroid/blob/master/COPYING.LESSER
 
 """Various context related utilities, including inference and call contexts."""
-
+import contextlib
 import pprint
 from typing import Optional
 
@@ -116,6 +116,12 @@ def cache_generator(self, key, generator):
 
         self.inferred[key] = tuple(results)
 
+    @contextlib.contextmanager
+    def restore_path(self):
+        path = set(self.path)
+        yield
+        self.path = path
+
     def __str__(self):
         state = (
             "%s=%s"

astroid/scoped_nodes.py

@@ -2190,30 +2190,31 @@ def ancestors(self, recurs=True, context=None):
             return
 
         for stmt in self.bases:
-            try:
-                for baseobj in stmt.infer(context):
-                    if not isinstance(baseobj, ClassDef):
-                        if isinstance(baseobj, bases.Instance):
-                            baseobj = baseobj._proxied
-                        else:
-                            continue
-                    if not baseobj.hide:
-                        if baseobj in yielded:
-                            continue
-                        yielded.add(baseobj)
-                        yield baseobj
-                    if not recurs:
-                        continue
-                    for grandpa in baseobj.ancestors(recurs=True, context=context):
-                        if grandpa is self:
-                            # This class is the ancestor of itself.
-                            break
-                        if grandpa in yielded:
+            with context.restore_path():
+                try:
+                    for baseobj in stmt.infer(context):
+                        if not isinstance(baseobj, ClassDef):
+                            if isinstance(baseobj, bases.Instance):
+                                baseobj = baseobj._proxied
+                            else:
+                                continue
+                        if not baseobj.hide:
+                            if baseobj in yielded:
+                                continue
+                            yielded.add(baseobj)
+                            yield baseobj
+                        if not recurs:
                             continue
-                        yielded.add(grandpa)
-                        yield grandpa
-            except exceptions.InferenceError:
-                continue
+                        for grandpa in baseobj.ancestors(recurs=True, context=context):
+                            if grandpa is self:
+                                # This class is the ancestor of itself.
+                                break
+                            if grandpa in yielded:
+                                continue
+                            yielded.add(grandpa)
+                            yield grandpa
+                except exceptions.InferenceError:
+                    continue
 
     def local_attr_ancestors(self, name, context=None):
         """Iterate over the parents that define the given name.