Provide options not merged from mixins

[jasonsanjose]

Version

2.3.4

Reproduction link

https://jsfiddle.net/jason_sanjose/00h2moa2/

Steps to reproduce

• Define a component A that uses 2 mixins that each define their own provide properties, e.g. foo and bar.
• Define a component B inside A that uses inject to add foo and bar properties

What is expected?

Both foo and bar should be available in component B.

What is actually happening?

The provide defined by the last mixin is the only one available.

Looks like the standard options merging only accounts for inject but not provide https://github.com/vuejs/vue/blob/dev/src/core/util/options.js#L185.

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Update docs if this behavior is expected.