add View.init_every_request attribute

tests/test_views.py

@@ -240,3 +240,21 @@ def test_remove_method_from_parent(app, client):
     assert client.get("/").data == b"GET"
     assert client.post("/").status_code == 405
     assert sorted(View.methods) == ["GET"]
+
+
+def test_init_once(app, client):
+    n = 0
+
+    class CountInit(flask.views.View):
+        init_every_request = False
+
+        def __init__(self):
+            nonlocal n
+            n += 1
+
+        def dispatch_request(self):
+            return str(n)
+
+    app.add_url_rule("/", view_func=CountInit.as_view("index"))
+    assert client.get("/").data == b"1"
+    assert client.get("/").data == b"1"