fix #11757 props on Object.prototype

[LongTengDao]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

I found that new ( Vue.extend({}) )() and components inside will work right, just void to new Vue({}) (root case), things will be ok.

So at least fix the propsData line, that will cause bug when prop is declared but no prop pass in (vm will get function on proto, not undefined nor default), that's easy to fix, and can't avoid like above in userland.

[sirlancelot]

I suspect you'll encounter many issues more than just this if your codebase (or other third-party lib) is polluting Object.prototype.

[posva]

I already answered this...