Create design doc for language splits dynamic apps. Needed for launch approvals M72 (feature freeze 9 Nov.) 

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The Design-Review issue type is intended to track tasks through the design
doc review process described at http://goto/chrome-dd-review-process.
Please add the design doc to be reviewed to the Design-Doc field.

Please review http://go/crbug-design-review-reference for steps on how to
move this bug through the review process.