[VK] Update docs for virtualKeyboardPrivate.setContainerBehavior.

The docs is wrong: the callback that setContainerBehavior takes also
takes a bool indicating success (see [1]).

[1] https://cs.chromium.org/chromium/src/extensions/browser/api/virtual_keyboard_private/virtual_keyboard_private_api.cc?type=cs&g=0&l=135

Bug: 902232
Change-Id: Ieead5072d7ab13c2b1cac1a8042b143fdd01eebb
Reviewed-on: https://chromium-review.googlesource.com/c/1354738Reviewed-by: Ben Wells <benwells@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612466}

extensions/common/api/virtual_keyboard_private.json

@@ -213,8 +213,14 @@
             "type": "function",
             "name": "callback",
             "optional": true,
-            "description": "Called when container mode is ready to chagne.",
-            "parameters": []
+            "description": "Called when container mode is ready to change, or if the operation failed.",
+            "parameters": [
+              {
+                "name": "success",
+                "type": "boolean",
+                "description": "Whether the container mode changed successfully"
+              }
+            ]
           }
         ]
       },